As has been mentioned many times.
Get a 1TB external drive - usb 3
Start copying before you go to bed - by morning it will be done. (You may want to change power settings in control panel to never put processor to sleep.
Then you've got a backup already - cost $50-70.
Other options are good - but this is best!

If you have a smart phone you might look in your "app store" for shutter release or photo remote.
Not sure if they support Leica - most are free or small fee.
The one I use for my Nikon has more functionality the the 3rd party one I bought

Couple of thoughts to consider-
- ANY teleconverter will degrade image quality to some point.
- any teleconverter will cause light loss based on their magnification.

Putting a T/c on the 28-300 may give you a better focal length - but depending on light conditions may to more tripod , or other stabilization techniques.

I wouldn't "step down" to the 5500 for a trip like this.

I have the feeling your camera is Full frame - if so consider shooting with the 28-300 - crop in post processing - you'll have a bigger image to work with

Last - if you have time - Try both ways - rent a Teleconverter and see how it works for YOU.
(Coming from a retired budget photog too)

First I doubt the flash is causing your lens flare - unless you were shooting close to a highly reflective surface

As far as flash coming on - I'm a nikon user so you can see how this applies to you -
If shooting in Auto mode the flash will popup when ever it feels there isn't enough light - so check your ISO - it may be too LOW for your conditions - the camera SHOULD adjust shutter speed and aperture to get the right exposure - if not BAM - flash should come on!
If in program, aperature, shuuter, or manual, mode it only pops up when the manually activated.

I flounder on this.

I shot 2 1/4 Sq in film days for a number of years - loved the format for the size & flexibility.
But I also understood that a portion of the image was going to be "thrown away" to fit into conventional print formats.
That was OK since I had a big image to deal with.

When I moved to 35mm I became a twister.

Sq digital would be good - but I don't think at aps-c, or even full frame, it would be a viable format - think I would rather twist.
"For that reason I'M out" - lol

Now if we could get an affordable 6x4.5 format I would be all for it

As a old film user I tend to keep 90% of what I shoot. I do cull out the obvious useless files (totally black, blown out, accidental shots of my foot etc.)
But I don't et lightroom manage it - I understand all their catalogue system can do - which is more than I want or need for my non-pro work. Also most of the issues I hear with Lightroom have something to do with the catalogue (I'm in a few lightroom FB groups)

I use Nikon Transfer to transfer my files from the SD card, create a folder, and rename the files.
Once they are transferred I normally cull out shots - then separate raw files into a sub folder. (I setup to shoot raw and jpeg of same shot).

When I'm ready to edit - if necessary -I open lightroom and just import the raw's I want to edit.
This works for ME - since some of the events I shoot I only need SOOC jpegs.

At some point I move folders from my I internal working drive to external backup drives based on the type of shoot (family, events, my passion work etc.)

This would probably be too labor intensive for a commercial, wedding, or portrait photog - but it works for me.
I can easily find image I shot years ago

You are absolutely right on the time involved in doing this type of scanning.

I didn't know about the unit you shared - but will definately consider it - a bit pricey - but depends what your time is worth!

I usually resurrect my scanning project when we get snow bound - lol

Been there! Still Am- lol.
I looked at the scanner you have a while back - only reason I didn't go that route was I also have 2 1/4 transparencies.

I did find a Canon canoscan 8400f that works for me. It is a flat bed scanner that has adapters to handle 35mm slides, 35mm negatives, and 2 1/4 negs & slides.
The plus is it will do 4 slides at a time.
Older and not the fastest but it works
((Older =bought it used in 2008)

As someone that photographs a lot of birds and is involved in a wildlife rehab group the concept bothers me - but that's a subjective feel.

Objectively - in my area we have a LOT of wildlife - primarily bird - shooters. Even a professional grade event in Feb - can't say I have ever seen the red dot "scopes".

The research I did seems to show they were popular on range finder/point&shoot cameras because of the small view finder.

I shoot birds in flight by setting to manual focus - zone focusing - and a medium aperature.
This has work well for medium to long telephotos.

Very nice stuff!
I do like your choice of subjects - and the way you captured them!

On the surf shoots - were you on the pier ir in the water?

I see your point and agree with the thought of learning the basics first. I'm not up on the Sony line - so can't advise on that particular camera.

But you know your grandson - is he REALLY interested in photography - casually interested - or saw the camera and thought they were cool. Nothing negative here just been there.

I'm assuming you wanted to keep him in digital - guess I would suggest a used dslr and see how he does.

I like the image. - but feel it's missing a main subject point. Some your eye is drawn too - my eye wanders over the picture looking for something to Latch on to

A friend has the Sony and im totally blown away by the shots he gets. Plus it will do 4k video

I rented the particular tamron you are considering.

I loved the lens - but it is a big hunk of glass.

I guess it depends how how light you want to travel vs adding another camera to your collection

Close to your age & experience so can relate.
I've been successful with eBay in the past - just look at the seller and see their reputation - also watch for sellers from Japan - nothing wrong with it - just you MAY have extra fees on top of the price and may take a bit longer to get to you.

If you need the longer focal length all the time then buy. But if you need it on specific occasions you might consider renting.
I use Borrowlens.com but hear luminoid.com is good to.
I have an older 70-300 I use frequently - but when the birds migrate through here I rent a longer - better lens.
(I shoot Nikon - but issues are the same)

For a variety of issues I've moved away from neck straps.
I haven't tried sling straps - yet

But for hiking and and general shooting I use a "Cottoncarrier" love it. Really takes the weight off the neck and keeps camera close to your chest and keeps it from swinging around.

Only negative for me is a bit slow to move to shooting position.