It's sort of a double edged sword.
On one hand, you want to book early (say, when the prices come out 8-9 months prior) so you can secure your date. But on the other hand, prices usually lower closer to the day of departure, but your day isn't as secure.
We booked over a year in advance (Feb 09 for a May 2010 departure) and the rates to go to RMB have fluctuated madly since we booked. Then again, prices for May 2010 aren't even out yet. The rate we're paying is kind of high, but then again, our date is locked in and the higher price sort of "weeds out" people who don't really want to be there for US.
If you're not picky about the date you're married, then by all means, wait until closer to the date. You'll likely get a good deal and everyone you want to make it, can come.
I don't really have any advice for booking bundles v. separatley, since we've booked through a TA who just did the group for us. Perhaps other brides will have better advice?