welcome to the forum.
for a start let the engine breathe more easily. a good induction kit and performance cat back zorst is a start. quite a few members have induction kits. some have worked better than others. (browse thro the search function to find the relavant threads)
Such as polopowah's which is a K&N, according to him, all show and no go!
GTI's work well with BMC
there are turbos out... 1 on ebay earlier. costs quite a bit tho
but its not worth spending loads of money to boost it to 100bhp.
instead invest in sum bigger wheels and coilovers so it ll handle better.. (IMO)
hope this helps
Cheers
Aaron