On some occasions I like to have 2 cameras when I walk an area to take pictures with a wide on one and extended telephone on the other. It's just a preference to changing lenses in adverse conditions (wind, sand, etc.) and can be fun. The problem is carrying them.

If I use a neck strap on one, then the other may be in my hand or on another neck strap. This can be irritating on my neck after a while and less convenient than I want. And the cameras can bang together.

Years ago I used a "hip side" belt clip with a camera attachment allowing the camera to slip in and out. While it was convenient, the camera mount threaded to the bottom of the camera (film) and in an L-shape pressed against the back of the camera. It was great and very secure. That camera clip, however, covers the screen on the back of today's DSLR's.

I had not thought of looking for a solution until recently when I saw a young female wedding photographer carrying 2 cameras at a wedding. The straps she used were slings. They looked like a great solution.

Amazon had a nice selection and I purchased two. They have quick disconnects and are extremely safe. I used them on a trip to South Florida to the Edison Estate. Quick and easy to use. Even if I only use one camera, there is no more neck pain and I don't have a camera hanging down on my belly. I like these slings and they are very comfortable.

Here is the Amazon link for what I purchased and a picture from their page. Tell me what you think.

https://www.amazon.com/gp/product/B00GR8KEMS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I fly with a Lowe ProTactic 350AW. It is a perfect fit for a "Personal Item" and goes under the seat. I put a D750 with 24-120mm lens, a D3300 with an 18-140mm lens, a 50mm lens, a 55-300mm DX lens, and a filter holder with a CP for each lens in a small carry pouch. Still has extra room for external pouches to store inside until getting to destination. There is a removable pouch for a tripod/monopod, and the other two external removable pouches. It also has a pouch for my MacBook computer and charger. Plus it has a rain cover stored in the bottom and a great waist belt with small storage compartments. This is not a "sling" pack but a great photo gear back pack. Very well thought out and extremely rugged, yet compact.

The airlines lets me carry an extra camera/case (keep it minimal) besides the backpack and my carry-on.

Hope this helps.

With that budget it is going to be tough to purchase brand new gear to accomplish what you want. I would suggest considering a Factory Refurbished camera. Here is an example: Canon is offering on their website, the SL2, a refurbished entry level DSLR for $398.00. This DSLR has some great features, and comes with a general purpose 18-55mm kit lens. For portraits you will want to purchase the 50mm lens with a 1.8 aperture for just over $100.00. You would be able to stay close to your budget. This is a good lens for portraits, at a great price. You can find something comparable in Nikon refurbished, but Nikon typically offers just a 90 day warranty on refurbished. Some will tell you to try mirrorless. It may be difficult to get a decent mirrorless camera and a portrait lens within budget. You'll want to go to camera store if possible, and handle various models to see what feels good to you.

Come on, it's Tony and Chelsea! They are decent entertainers but not exactly the be all end all authority on all things photography. They have a nice YouTube show and make some nice videos and I like their educational material but, Tony can be a doom and gloom naysayer sometimes.
What exactly does, DSLR'S are dead mean anyway?! Are DSLR'S on the way out? Yes. Just like digital took the place of film, MILC'S will eventually take the place of DSLR'S. But what difference does it really make?! It's still digital photography with digital cameras.
I shot a child's birthday party recently with my Canon 5D mk IV. I got some really nice photos. This little girl looks like Shirley Temple. Anyway, the camera worked great and the images are really nice. No amount of Sony or Panasonic or Fuji or Nikon or Canon MILC'S will change that. People are making such a big deal of mirrorless cameras because they have a need to justify spending money to replace something that worked fine, in a lot of cases just for bragging rights or, they are using this normal progression in technology to further their own recognition.
Cell phone cameras have taken a big bite out of the dedicated camera industry, but they haven't killed it. For casual picture taking, cell phone cameras are fine, but for serious photography? Come on, get real, do you really think the tiny lens and the little sensor can truly out perform a good dedicated digital camera or most any MILC or DSLR? Not likely. How many people do you think do astrophotography with their cell phone? Probably none. Cell phones may dominate the snapshot world but they're still in the back seat when it comes to serious photography.
Will I ever buy another DSLR? Maybe, I don't know. Depends on what the manufacturers are offering. Will I ever buy a MILC? Already have. Not a full frame yet, a Canon M50. Nice little camera, kinda small but nice images. I looked at the EOS R but it doesn't really give me much that my 5DIV doesn't already. Sure, it has some nice feature the older camera doesn't but it's got the exact same resolution and for now I can live without the features it does offer. Plus, it's bleeding edge technology. Maybe when Canon drops the price to move inventory.
No, DSLR'S are not dead. Production of them will be phased out as demand and profits drops but the millions upon millions still in circulation will continue to work for years to come.
A while back someone posted something about Canon going under because Sony has cut into their profits, big time. Problem with that is, cameras are not Canon's only source of income or even their main source of income. LaserJet printers, and not just Canon LJ printers are a huge source of income. One of the largest if not the largest maker of LaserJet printers is Hewlett Packard or HP. Every HP LaserJet printer has a print engine made by, Canon. Sony doesn't make LaserJet printers. Canon even makes hospital diagnostic machines such as CT and MRI scanners. Sony doesn't make medical diagnostic machines. Some of the best, if not the best cinematography lenses are made by Canon.
No, Sony's mirrorless cameras are not putting Canon out of business and DSLR'S are not dead, and they don't drool either. Technology marches on, deal with it. It is what it is, and not the end of an era, more like the evolution of a technology.

1. Yes, <auto> is a good starting point
2. No, the WB is determined by the camera, either via a AUTO-WB setting or something the photographer (you) set when capturing the image. There's nothing about the JPEG format that impacts the WB of the image that is different than any other image file format.
3. I use an older version of LR. I've seen comments that Adobe has improved the intelligence of <Auto> vs older versions. A subscription user would need to comment.

Regarding an edit workflow. Personally, I import all my RAW images into LR and the apply Develop Presets I have developed that accomplish:

a. Apply the lens profile for the lens version used.
b. Set the camera profile to Camera Standard.
c. Apply ISO-specific noise and sharpening values I've developed for my individual cameras.
d. Apply default values of Clarity, Luminance and Saturation I've developed for my individual cameras.
e. Trigger Auto WB and Auto Develop.

Before editing, I try to remember to add keywords and move all images to a collection in my library. This can be done later, but I've found it best to do this admin work up-front.

I then begin editing images individually, with the images sorted by capture time. Given I have a string of images, they’ll typically be from the same lighting situations. I edit the first to my desire, moving / correcting the individual sliders on the first image. LR's <auto> is what might be called a "disaster" relative to both the original and the final version. But, the ideas of what to correct are useful, many times giving ideas I would not have considered by myself.

When I finish editing the first image, I then use the ‘power’ of LR by syncing the settings from the first edit across the next similar images. Sometimes, they’re all good or they require individual, but minor, addition tweaks. Sometimes, I sync those additional edits back across all the images, other times the images remain unique. It does depend.

"Syncing" is done by selecting multiple images from the film role in Develop, or the Grid in Library via Sync Settings. You can uncheck all and then select just WB and Exposure, or whatever specific setting to sync. So whether you start from Auto or just the imported version, the power of LR is the syncing function across similar images where every image doesn't have to be edited from scratch.

As you edit, use the backslash "\" and flip back n forth from the original to the current status of your edits. Sometimes the history panel is useful as I have at least three points of reference: initial import, application of the preset triggering the auto develop and auto WB, and the current status of the editing.

Use utube videos or your books for examples and explanations for each slider. As <Auto> doesn’t touch Clarity, Vibrance and Saturation, my presets apply values for these sliders.

I first get the "basic" edits of the exposure and White Balance completed, then give a second pass for cropping, cloning or anything more complex. I also tweak noise and / or sharpen and sync these refinements across similar images, using the syncing function and updating the parameters being synced to just these settings.

I use the image compare tool throughout the process to identify and discard duplicate or inferior images, setting them to rejected and removing from the edit session. If I do my work from within a LR collection, I can periodically filter by rejected images and remove the rejects from the collection without impacting their status in the Library. At the end of the session, I delete all rejected images, both from the catalog and from disk.

Regarding my (a) to (e) preset actions, you can do these manually in-mass from the Library module as well. Use your Metadata filters to identify and isolate images by cameras and / or lens models. You'll then update one image with the lens profile and camera profile (Camera Standard or other) and sync those settings across all images from the same camera and lens.

LR Question; still in the early days of getting used to its capabilities. Would appreciate feedback on the use of the Auto correction under "Basic".

1. Is Auto a good "starting point"?
2. In going through JPEGs from 2017 (I was new in using a DSLR and not aware of RAW) all the images become "warmer" when I have chosen this option. Does this say something about shooting in JPEG or more to do with my lack of experience when taking the images?
3. On those where I have chosen to use Auto, the outcome is not substantially different to when I initially went through utilizing the LR tools; remember I am still learning the tools and techniques from the multiple ideas on process steps from third party more experienced users