RS2 brakes on to an S2 is very straightforward.
You need the RS2 caliper brackets, a set of RS2 calipers (either the standard, which take a 304mm disc, or the "Big Red" ones which take a 322mm disc).
Disc wise, if you've got Big Reds, you can get the stock Audi A8 322mm disc. If you've got the 304s, my solution would be to buy the A8 314mm discs and have them turned down to 304mm by a decent garage.
Get the RS2 hardline brake lines and get a couple of litres of ATE Super Blue brake fluid.
Pad-wise, my recommendation would be the pricey, but can't be beaten on any way you measure, the Ferodo DS2500 pads.
If you go to s2forum.com there is a wealth of information around other "off the shelf" brake upgrade routes which you might also want to consider, including getting the Porche Cayenne 8-pots on there!
AS far as getting an S2 engine up to 310, it's relatively straightforward. You need the RS2 turbo, the RS2 manifold and a remap from MRC. If you invest a bit extra in a bigger intercooler, metal head gasket and injectors, you can easily and reliably see 350bhp from the same block. Going above 350 it is recommended to get strengthened rods to cope with the extra power and torque.
My best advice to you is to lurk on s2forum.com
