Exciting stuff!

Suspension and chassis:
Have you recently replaced ball joints and pitman/idler arms? And are you using factory LCA's? You could brace the LCA's (AR Engineering kit from firm feel). You could also weld up and brace the k member, if you want to go so far as to take it out (AR engineering kit from firm feel)

Brakes:
I'm not familiar with the piston sizes in those brembo calipers. The cobra calipers are well sized for the rear. I would recommend no distribution block. Just a straight line back. And a t fitting for the front.
Find out front piston sizes and run the math sheet.
Your master may be fine. I run a 15/16 2 bolt I got from dr diff. The 15/16 might be a better size for you. Though If I were you, I would start with the master you have and change if you feel you need it after running.
Rear brakes: I run braided lines to my rear calipers for ease of working on them. Did dr diff send you a set? If not, see if the front braided brake line part number will work (I used same PN braided on all 4).

Wheels:
You're going to have to nail your back spacing if you're going to get 275/35/18's to fit square. I'm unfamiliar with 2 piece wheels- but don't you need new cylinders to change offset? Sounds expensive to swap sets?
What size wheels do you have now? How do they fit?
I run 265/40/18 square on the street (I like the taller tire), and 275/35 fit as well. I'm running +45mm offset in the front(7.2" back spacing), and they rub the frame and the wheel well at about the same time (around 1.25 turn of wheel). I lost turning radius. If you don't go so low, you can run less offset.
The rears are tight as well both inner and outer wheel tubs have tire rub marks from tire rubbing. 60.5" width rear with +45mm offset there as well. Also running dr diff offset leaf spring hangers (would be in leaf springs if not)

Cheap way to find perfect fit is to get a high offset wheel of the size and tire you want, and use spacers until you find the 'perfect' location in the wheel well. Subtract the spacer width from the offset and you're done. Where are you located? I have a 18x9.5 +45 spare laying around.

Hope that helps a bit.