What's a reasonable model with a semiautomatic workflow (that I don't have to work manually frame by frame) for that? A 5000ED or something like that?

I could do that for my dad too...

Slides are going to manual because they’re (usually) individually mounted.

I haven’t seen any consumer scanner that has an auto feed. Good ones have a nice sprocket wheel but you still feed manually with a wheel.

You can get a slide feeder for the “modern” (early aughts) Nikon Coolscans, the SF-210:

https://studio-supplies.com/products/nikon-sf-210-239995

The slide feeder is good but it's worth being aware that if you have slides mounted on cardboard (I had a lot of old family photos like this I used it for) it will often grab a couple at once. You can fix that by clipping eg a driver's licence in the right place to narrow the gap it pulls the slides through, but it will still need some manual supervision.

If you get one, have a look at VueScan on the software side - the original software needs (I think) a Windows XP virtual machine to drive it.

Yes this is all true but it works well when you know how to deal with these issues. I suspect aging slides would be an odder for any automated system.