Mike,
Just a suggestion. If I were you I would go ahead and put in a stock motor and get the car running/driving, then start planning an engine build. Sometimes it's just best to keep it simple starting out with something like this. Besides, a stock motor will make plenty of power to keep you happy for a while. Mine is just the rb25 but still stock and makes almost 500 rwhp on pump gas. The same mods on a rb26 would make even more. Also, (keeping it simple here) I would (did) personally go with one large turbo. Twins look cool but just complicates things IMO.
Just my 2 cents, for whatever it's worth.
JT