It’s always hard to figure out fair prices for used unis, since there isn’t really any comparison. Also, look at the condition, and do the full math, replacing a bunch of small wear items (tire, bearings, pedals) can add up.
If you don’t have a lot of hills where you ride, a well setup rim brake could be all you “need”. If the deal is good, saving some cash for everything else that you might suddenly need for touring (bags, clothing, etc.) might be nice. I’ve personally noticed quite often those small things can have much more of an impact on my riding experience than a higher quality uni.
If you are looking at buying new, I’d consider other brands too. (look at this thread: https://unicyclist.com/t/opinions-on-best-36er/ )
Depends on what rim brakes you are talking about. If you are talking about a set of v-brakes or calipers, you need less tools to repair them and set them up (an allen key is pretty much all you need usually). I think from a difficulty perspective, rim and disk brakes are equally “difficult” to set up, they just have different problems.
If you are comparing to Magura hydraulic rim brakes, you’ll need to bleed them just like you would on (hydraulic) disk brakes, so you’d need to buy a kit for that. Bleeding them is a bit of a learning process, but not too hard either, or if you don’t want to do it, it’s a pretty standard and cheap thing to have a bike shop do it (every 2 years or so should be fine for a 36").
I used to think that disk brakes are fiddly and difficult too, but my experience with them has been the opposite. Set them up once, change brakepads/disk when necessary, no trouble inbetween.