1: C2Q's are still sufficent; an i5/i7 build (Nehalem) will "last" for two years, but you likely won't have significant upgradability should you go that route, ESPECIALLY on 1056.
2: Right now, I'd WAIT. With a socket change in the VERY near future (two-three months), a new intel arch, and very promising benchmarks, it doesn't make sense to make a new build that is meant to last. Nothing quite like buying a Pentium 4 right before the Core 2's dropped, after all...
3: AMD is VERY tight lipped about BD. That itself is VERY worrysome, as AMD has been very good about leaking benchmarks...when they beat the competition. And given how Phenom I = C2D, Phenom II = C2Q, I suspect BD = Nehalem. If thats indeed the case, and SB is a significant performance upgrade, AMD could be left significantly out in the cold.
Right now, I would just wait until we start seeing more benchmarks, and get an idea where performance for SB will land.