C and PF Positions/Roster Spots in general
I agree that after Moran and Perkins, there is a big drop in talent at the C/PF positions. To me, those two are locks to make the team, and have major roles. I do think it is important, though, that they have at least other C/PF type supporting them (even in the early games). I would expect to either have one or two of the weaker big men on the team to start. Since the options here are very close in current skills, I would consider likely development during season 12 in deciding which one(s) to put on the opening roster.
Looking at the opening roster size more generally, I expect to star off the season with either 10 or 11 players (I haven't fully decided yet). I do like the extra resilience during games that comes with 11 players (as foul outs and injuries can happen any time). I would want to be up to a full 12 by the first difficult game, but as Aston Midhurst points out, there will probably be some one-sided games early on, which allows for holding some spots open for awhile.
While on the topic of roster size, My current plan would be to use up to 3 roster spots for saving prospects throughout the season (ideally, in the earlier weeks). This would leave 4 or 5 spots for callups throughout the season, if the roster starts out with 10 or 11 players.
Own players on U21 team
Chris asked a question about what managers would do if they had players on their league team that are eligible for the Canadian U21. My short answer here is that I don't have any Canadian U21 prospects, and probably won't in the upcoming seasons. If I do end up acquiring a U21 eligible player, I would treat that player the same as any other, in terms of making the team and what role they might have on it.