Yours isn't ABS is it? If so then you wont need valving, it'll balance itself.
If not, then....well, see how you get along on the track, if you're locking up on the rear then, well, you know better than I how to tweak such things.
I have no idea on that stuff though, all mine have been ABS.
As for the callipers....again, see how it goes, unless you panic-brake mid-corner then you shouldn't have any problems as, again, those front rotors will suck up everything you throw at them. Remember, Flyin Miata was using them on their V8 conversions (which aren't much heavier than your set-up, but at 525hp....yeah, they can get a workout)...
....actually, I've seen V8 Conversion Mk.1s using the MK2.5 Sport brakes, just with "fancy" pads, good fluid, braided lines and solid, vented discs. The supercharged Mk2.5 at Hunstanton was definitely just running stock callipers and he said it took many laps of Cadwell to give him any problems