the XT drivetrain should be great.

I would also go with a disc on the front: get the Avid bb7 Road mechanical disc brake, It will work with brifters and is a well respected brake. A canti on the rear will allow the brifter use without any goofy V-brake adapters.

Make sure your cassette and brifters match. Its getting harder to find 9 speed brifters, let alone 8 speeders.

I used that nashbar fork on my crosscheck and liked it, even though it was heavy. It was pretty stiff and steered well. very beefy!

Sounds like a fun bike you're building, enjoy it!!