Im an Enduro rider but i had some of the same challenges as you when I chose to start riding again after 20 years.

• look at what dealerships sell in your area. A friend of mine bought a moto guzzi and it was a fantastic bike but only one dealership existed in a very large territory that offered parts. Whatever brands local dealership sells will proportionally indicate part availability.

• maintenance for most motorcycles can be broken down to similair components. Fortnine has a video on tearing apart and putting back together a motorcycle and a general indication of the fundamental components to expect to deal with. As fancy as a bike is, there's ultimately a finite amount of things you will deal with. Also if you can find it, grab yourself a physical copy of a repair manual. It's nice to have for even dumb little things.

• depending on your maturity, I would consider something between 500-700cc. Most people I know who have bought a sub 500cc bike end up selling it again at a loss in a very short period of time. I ended up buying an 800cc as my first bike. I took riders training again, and had several years of driving under my belt. I dont have a need for speed and ive never had an issue with being unable to control my bike. But if you decide to go on a highway with your bike, having the jam to speed out of a sketchy situation becomes another tool in your kit.

I really like fortnine's videos when it comes to perspective on bikes, and gear. I watch a lot of videos regardless of how long I've been riding. Here's one on beginner bikes.

https://youtu.be/ifBNDeMZQkI