I swapped the master cyl too but was told it was not strictly necessary. The wheels basically need to be similar to the 996 Mk2 GT3as that what you now have on the front. I have 8x18 ET42 with some 3mm shim spacers and am having some new ones made to ET40. I guess it depends on what your current wheels are as to what spacers you need.
I am pretty sure mine are 355mm disks but you have a 100-150kg advantage over a gt3 so there is plenty of headroom
