As the insiders have said multiple times, RJ is basically a guarantee to start. You don't start McCullar but with his size, versaility, and defensive abilities he is in first rotation and can sub out anyone from the 1-4, and because of that will get starter minutes. Also, because of his defense, he may not start games but he will be in at the end of close games.
In a lineup with McCullar and Nance added I believe:
Skyy
TSJ
RJ
Coleman
Nance
With McCullar, Dain and Ty all being the the first rotation that BU likes to do at about the 15/16 minute mark. McCullar can sub anyone 1-4, Dain can probably sub either Nance or Coleman and Ty can sub anyone 2-4.