Re: brakes - stock is very good. Pads alittle soft and messy.
Stormcat, Shadowman, have done "big" brake changes, give them a call.
Stillen offers a brake upgrade also. If they have any left, a 3.9 crown gear in the differential makes driving the GT quite a bit more enjoyable.
With you larger wheels there are options that are availiable.
And not knowing your driving background (other than your brieft mention of past fleet vehicles) a h.p. driving school would be a great investment.
Followed up with as many track days as you can schedule.
Most of all drive it often. Radio off, windows down. Great music from the back end!