Hi mate
welcome, i myself am only 3 weeks into onwnership..........simply awesome!
Ive had Fiat Uno Turbo-RS Turbo x2-Golf GTi-Renault 16v. Nothing gets close to impreza ownership mate, i cant stress enuff how much you gotta get yaself one.
As for things to look out for have a look at this (if u aint already) http://www.sidc.co.uk/faq.htm
When lookin for mine i just applied the age old stipulations of FSSH (plus other bills etc), least amount of owners u can find, HPi, unmodified (engine), Unkerbed alloys (shows a carefull owner).
I was lucky, i found a minter straight of the bat (with a couple of nice mods).
Take ya time, and dont rush into anything....its easy to fall in love with a car and get carried away.
Sean.