I've had pretty good success with Lenovo's recently. All of my computers that are biting the dust are being replace with budget Lenovo's. And the timers on my crew love them!
I'd recommend buying new if possible
(i.e., less wear and tear; you know the condition of the hard drive; warranty issues, etc.)1) Maybe not necessary quite yet. But probably a good idea. I love Windows 10 compared to Windows 11. But you gotta remember that learning new operating systems take some time. It will be necessary sooner or later even if it's not necessary right now. AFAIK, ART will still run perfectly on Windows 10. But who knows how long for if Windows isn't providing updates for it?
2) Partially answered in part 1. It's not necessary but it's probably advisable as you don't wanna wait to learn Windows 11 until the time comes when you're forced to (and you'll want to be spending your time doing other things, e.g., family, timing prep, actually timing). There are major differences between W10 vs W11. I'm still getting used to the Windows 11 layout, even though all of the new computers I've bought over the past 12 months have been W11 computers. My main computer (which I'm using right now) is W10. So I'm not as gungho about learning everything about W11. But eventually I'll be forced to use Windows 11, so it's better for me to start learning now.
Overall, I think buying a used W10 laptop might be fine. But there are obvious drawbacks (e.g., you don't know if it has issues upfront). And support will end at some point. So if you're timing a lot of races, you don't want the learning curve to start in the heat of your race timing season. On the flip side, being able to learn W11 while you're using a W10 main laptop is a great way to learn the differences and to overcome a steep learning curve.