Go ahead and set-up an app specific password. I have several email accounts, including several different Gmail accounts, so I use Microsoft Outlook to keep them all straight. To use Gmail with MS Outlook you need to use app specific passwords. I have used Gmail this way for many years, despite getting doom and gloom warnings from Google about every 6 months, about "security issues". I have never had a problem. Just be sure to use strong non-guessable passwords.

Apple Photos is primarily a photo organizer, with some editing tools. Lightroom is also a photo organizer, however it includes a raw converter, which enhances it's editing capabilities. Photoshop including Photoshop Elements are pixel editors, they are able to change photos at the pixel level. The answer to your question depends on what you are using to capture your photos. If you are using a Mirrorless or DSLR camera shooting in raw using a raw converter like Lightroom, or Adobe Camera Raw in PS or PSE makes sense. If you are using your iPhone as your camera, Apple Photos can handle most tasks on your images. If you want to get into compositing (using parts of more than one photo to create a final image) then you want Photoshop or Photoshop Elements. You may also want a stronger editor if you plan on making large prints from your photos.

Adobe introduced colorization as a guided edit in Photoshop Elements 2020. It did not get a lot of fanfare, however since I need to occasionally colorize an image, I bought PSE 2020 despite being a Creative Cloud subscriber. I have worked with the AI based engine in PSE and the new beta engine in PS 2021, as well as trying some of the online options. Some thoughts:
1. While AI does a good job at finding and colorizing faces, it frequently misses areas of an image, or colorizes them radically incorrectly.
2. Both PSE and PS allow masking and spot color picking to allow a human to identify and colorize areas of an image that AI misses or gets wrong.
3. At this time PSE is a little better than PS at finding and picking colors.
4. The select and mask tools in PS are much better than the same tools in PSE
5. PS outputs to multiple layers, where as PSE places the results on a single layer. Having the colorization on more than one layer simplifies the future workflow refining the image and making the results look more realistic.

Just my thoughts

Great scanner, I have the earlier model the V550. If you are on Windows the Epson software will work, however you can go to the Epson support site and it will take you to a link for a free download of SilverFast SE. You will need the serial number off your scanner, to download and install, but that is the better software to convert negatives.

That explains so much. The method using a hack to scan with a flat bed scanner rarely works well. First the negative needs to be held flat, usually requiring some type of negative holder. The platen on your scanner will not itself flatten the negative enough. The scanner will pick-up any texture in your reflector through the negative or transparency. I'm seeing both problems in your sample image. I'm not sure the original size of the negative, but you may need to create a negative holder out of cardstock to hold the negative flat. Once it is flat, place it over a diffused light source and photograph it using a digital camera. Then use PSE to invert the image. Note if the striations are still there then they are scratches on the emulsion layer of the negative. The dust and scratches filter in PSE should help.

A better option would be to use a photo scanner like the Epson V series. Although, they look like flat bed scanners, they have negative holders and a top down light source for handling negatives and slides. Current models include a license to SilverFast scanning software, which can handle the inversion of negatives, as well as clean-up dust and scratches in the scan.

Check with TetherTools and get the correct cable and jerk stopper. Tethering into Lightroom Classic will work, but it's my understanding it does not support Live view mode on a Nikon. It is painfully slow on my Canon cameras, so I use the Canon EOS utility. Unfortunately Nikon sells their live view tethering software separately. I did a a trial of Capture One 20 just before Covid hit. It handled the tethering tasks extremely well with my Canon DSLR, and from what I have read it works as well with Nikons. Without live-view, you will need to set, take a test shot, analyze, correct and take another shot until you get it right. One added bonus with Capture One, is you can turn on focus peaking on your live-view to check critical focus.
Your lighting panels seem more than adequate in size for most objects. From a time perspective, setup your copy stand and lights to evenly light the baseboard of the stand. Then move art in set camera position to fill the frame with the object, check critical focus and shoot. Onto the next piece. For the larger pieces you may need to work vertically on a tripod, and may need to augment your LED's with your strobes, which means lots of test shots to get it right.

The standards just addressed image quality levels. For 3d objects I would focus stack, if you have software to support compositing the image, however you want to keep all of the original master images, as well as the stacked composite. In absence of a camera and lens combo that supports stacking through autofocus, I would use a macro rail, rather than trying to adjust focus manually.

The striations look more like scratches rather than dirt. What are you using to scan and what software are you using to invert? For cleaning I use a Rocket blower and PEC pads. For extremely dirty negatives I use PEC12 sparingly. I do take a scan prior to using PEC12 as it can easily make the situation worse.

5600k and 90 CRI sounds good, however how big are they? With lighting remember it is not key and fill, you need to have controlled even lighting over the entire surface, no shadows. You also need to have enough ambient light in the room to work, but only light from your light source should be part of the exposure, to maintain proper color balance. Keep in mind you may need to resort to diffusion panels or a light tent depending on the situation. Therefore, tethering is essential, and live view tethering is necessary, so you can monitor your lighting as you are setting-it up. It is also helpful for verifying critical focus.
As far as lenses go, macro lenses are designed to be sharpest at their closest focusing distance and have even sharpness across the field of view. Traditionally, telephoto lenses and telephoto zooms are designed to be sharpest at infinity and allow some fall-off in the corners. Since your normal working distance to your subject will be 4 feet or less, the 55mm macro is the logical choice. In instances where the objects are small and the camera is interfering with the lighting, then move to the 105mm macro to back the camera off the subject.

Photoshop CS/CC etc. has the capability to open a pdf file and extract images. It has had this capability since at least version 4. Early versions of Photoshop Elements also had this capability, but Adobe removed it some where after version 8.

Welcome to the world of “Cultural Heritage Photography”, which involves the digitization of art and other objects significant to cultural heritage. Many museums subscribe to the “Federal Agencies Digital Guidelines Initiative”, otherwise known as FADGI. The technical guidelines are available here: http://www.digitizationguidelines.gov/guidelines/FADGI%20Federal%20%20Agencies%20Digital%20Guidelines%20Initiative-2016%20Final_rev1.pdf
For the art you are attempting to digitize, note the table on page 46. Most of this work is currently being done using medium format digital cameras from Phase One or Schneider using specialized motorized copy stands, Special versions of Capture One, which can control both the camera and the copy stand. Preferred lighting is continuous as it is easier to check lighting.
With your D600 you will only be able to achieve level 1 or at best level 2 images. Photographing the art horizontally using a copy stand is easier than vertically, as you need to set lighting and exposure prior to photographing the art. Tethering is essential, and live view tethering is necessary. Capture One is probably your best software to handle the tethering on a Nikon. Use an X-rite Colorimeter along with the Passport color checker to calibrate your display. Then use the X-rite Passport Color checker to calibrate your camera and lighting. You will also use it to adjust your exposure. You want to include a small IT8 target in your frame with each master file.
Pick-up a resolution test target like the USAF 1951 and find the optimum aperture. Your workhorse lens is likely your 55mm Micro Nikkor. Your 105mm will be useful for smaller objects. Do not use your 70-200, it is not sharp enough in the corners. For camera settings, base ISO, aperture optimum for your lens/sensor, use shutter speed to balance to correct exposure as determined by the Passport Color Checker.

You need to use Silverfast SE when you scan. Epson has set up a free download program for V550 and V600 users. Go to the V550 support page at: https://epson.com/Support/Scanners/Perfection-Series/Epson-Perfection-V550-Photo/s/SPT_B11B210201?review-filter=macOS+11.x and follow the link.

Have not used one or the other but have been looking at the specs for a long time. In the 8200i the I stands for infrared. Using SilverFast software, the scanner will perform a second infrared scan of the slide or negative and use that information to automatically fix dust and scratches. Although, it increases the time to complete a scan of each frame, it saves an immense amount of time in post-processing to clean-up dust and scratches. The feature works with most film stocks, except for Kodachrome.

I found a piece of software specifically designed to correct color casts and poor contrast in scanned photos. It's called Restore by Vivid-Pix. Prior to using Restore I used levels and curves to correct color casts, usually in my scanning software when I scan the image, or in PSE / Photoshop when someone else completed the scan. Here is the one click result from Vivid-Pix Restore.

(Download)

I think everyone so far missed one important point, Lightroom Classic or Lightroom does not change any file upon import, be it TIFF, JPEG, PSD or any supported RAW file format. With any file you import Lightroom builds a JPEG preview. Lightroom stores the edit information in its database, so if the JPEG preview is lost, it can be recreated from the original and the edit information. When building the preview Lightroom uses a flattened version of a TIFF or PDF file. If you want to re-edit in Photoshop, you must use the option of EDIT original to get the layer information the file was saved with. Edit in Photoshop will send fresh copy with Lightroom Adjustments back to Photoshop.

I know that was basic, however Adobe greatly increased the minimum system requirements by requiring a 6th gen or new processor and DirectX 12 for Elements 2021. Elements 2020 was more forgiving on older, underpowered computers.