Re: BuddyPress and Shared Hosting
The reason that the specific question of the OP is a WPMU issue is that he was asking whether a shared hosting account will be sufficient to run BP. Since BuddyPress is a WPMU plugin, what matters, then, is whether WPMU can successfully run on a shard hosting account.
I provided several links for him to begin his education.
In short, of course you can install WPMU + BP + bbP on many shared hosting accounts. But, whether that will provide a desirable user experience or support more than a few 10s to 100s of active users depends on too many variables to be discussed here. The underlying functionality of WPMU is paramount to the overall site functionality. If your site’s access to server resources is too limited, you will have issues quickly.
Perhaps once BuddyPress supports single-user WordPress, the options for hobbyists, as you call them, will be better.