if your going for more than standard power there are a few options available to you braking wise -
keeping with standard 239mm, mk2 GTI 16v Servo and 22mm master cylinder, braided lines, grooved and drilled discs, and something like EBC greenstuff pads.
or,
G60 brake conversion, although the brackets for this are a bit pricey, im sure they can be knocked up cheaply enough if you had em custom made, its only a small bracket at end of the day.
my valver is running similar power at the mo, and im going for the first option.when i go over the 200bhp mark ill upgrade to g60 brakes all round.
gearbox wise, standard 020 box should be fine providing its in good health, but obviously your going to want an uprated clucth.
hope that helps
Dean