rebuys...i hate those bloody things
before the add-on break, you can be either the really tight guy that values his buy-in and takes advantage of the 15-rebuy maniacs and their loose calls
or you can be one of those maniacs yourself...which actually isn't such a bad idea - you play generally looser than you normally would and hope to double or even triple up and have a nice chip stack going into the break. Obviously this costs way more and is the more aggressive way, i guess you could say
after the rebuy it tends to play more like a normal tourney
anyways in response to your actual question
i don't know if there's a specific number of rebuys you should have available but it depends on what style of play you're leaning towards i guess