BuddyPress, bbPress, forums plugin and starting a new site?

I'm starting a new WPMU (soon to be 3.0 site) and I don't expect to be using any BuddyPress or bbPress features for a while, at least. Maybe 6 months or more. But I do expect to want to start using them at a later date.

Is it smarter/easier to install WPMU and BuddyPress (or bbPress) all in one shot when starting out, or can I just as easily add them in once my site's all populated with articles and users?

Next question: do you have any expectation, when moving to 3.0, of BuddyPress day-and-dating the 3.0 release, or is it likely to follow on months later?

As for the forums plug-in -- same idea. Can I just add it whenever, or is it better on a bare-bones new site?