welcome chap.... i dont own a evo X, so not too sure on what to look out for on them tbh, somebody else will probably comment....
but when buying make sure its been well serviced, and maybe look for a private seller, they can be better looked after... its not always possible but try and get a good look underneith to see what condition the chasis, sub frame, roll bars etc are in.... some owners can look after them well and keep off salty roads etc...
when you say what to buy for it, i would get used to it first before you start spending.... first thing i did was get some decent performance friction disks and some better break fluid in the car as i kept boiling it