www.sidc.co.uk
www.scoobynet.co.uk
Personally, I'd go for UK spec Turbo rather than import WRX - the amount you'll save on insurance and the fact you can service it at a Subaru dealer more than outweighs the theoretical performance advantage of the WRX/STi.
(I say theoretical because unless you're used to 280bhp and/or intend to go on lots of trackdays, you really won't know the difference
).
I'd go for the 99my if you can - slightly better performance,
much better brakes, better headlights - you can identify the 99my by its slightly revised front end.
Steer clear of heavy performance mods - they'll kill your insurance (and your engine and/or turbo if not done right).
When you've got it, join SIDC (Subaru Impreza Drivers Club), for meets, advice, discounts, new friends! etc etc.