I bought it for 230 euro used, pretty much new condition, the seller had always used a screen protector and a case for it.
Everything you are saying about "android os" is pretty much false, no it wont get slow if you aint a dumbass and dont download excess shit, else just reset your phone if that happens and I can find parts and other accessories for my note 4 which is 3 years old.
Adding even more salt to the injury, you can root your android device, replace the os with a custom ROM if you are in need of it, do a lot of customization like remove pre installed apps and shit like that.