ive jus put an xr2 lump into my mk4...exactly the same as a mk3 i assume, i had to make my own loom for the ignition as my engine ran off hcs management, but urs shud all jus plug in nice and easy.
as for big power ive seen 180 bhp cvh's u can pick up for about 800 but if u got the cash go for the zetec theres alot of guides etc hoe to fit them on here