don't really know why so many are so eager to get the popping and banging, but might be due to the fact that these cars are getting silly cheap over there in the UK.
anyway, there have been quite some discussions over this and seems the golf will always pop more than these cars.
I run a decat as well and 2.5" exhaust and am happy to report no popping or banging
As for power, I'd invest in one of the THS universal intercooler sets of approximately 150 quid (or something like that). That will allow you to keep your power better in high revs.
As for more, you could go stage 2 but then I would advise the K03s. That will give you the extra 20-30HP, but on 500 quid you won't make that.
My advise, get the FMIC and a TIP and you're done for 300 quid. should see a good 200-210hp (max)
and a search would have told you all this