Fantastic cars, and a good combination between luxury big car feeling and rawness.
Still regret selling mine, but i was skint at the time

hold out for a later 6spd version as they have a touch more power and map slightly higher. They also run individual coilpacks and a DMF making the a bit smoother to drive. Have heard the earlier 5spd 3B versions can feel a bit more raw to drive (not a bad thing!)
A couple of things to note though, it wont be quite as quick as an E36 and definitely wont handle as well in stock form. The engine position makes them very understeer biased. It is worth finiding the period german sport auto or autobild article (cant remember which) that ranks the s2 ahead of both the e30 m3 and the merc 190 cosworth.
avants have more advanced rear suspension and look better

fuel consumption is quite high, but then again it is on all proper cars.
General basic servicing isnt too bad, but some of the s2 specific parts can be pricey or NLA from audi.
the I5 on song sounds great.
280 is £250 away with a chip from s2central.
anything else you want to know, i'l do my best to remember, but basically, DO IT.