The rotations won't be shortened as much as you think it'll be shortened. All 5 "main" subs will play right off the bat. If one or another start sucking for one reason or another, then they'll find themselves in the bench more often than not. I very much doubt there's a game plan to just come and shorten the rotation because I'm pretty sure Doc wants to use all 5 of the bench guys.
It has been pretty much this way for the past 2 seasons during the playoffs. Exceptions were Eddie House and Tony Allen. The later pretty much because of injuries late in the season while the former with his lack of height and ball-handling skills made it difficult to just play him in certain match-ups/situations ahead of a PG who can actually handle the ball. I don't see that being a problem this year, other than with Nate getting abused for his shortness, but he has ball-handling going for him.
In all, I think a lot has to happen for the 5 bench guys not to get minutes I think. I think Nate has the shortest leash though.
He's generally gone with an 8+ man rotation, with the "+" being the 2nd big that gets 8-9 minutes a game. It's hard to say whether it's by design or necessity.
As for Marquis, it's hard to say what his role is. I don't think Nate is a great playmaker, and he won't be able to stay on the court long if everyone's able to post him up.
Not early on. He starts off going with his full bench cycles or with 4 subs at the very least, until they start sucking.
In 2008, it was Davis and Powe dropping the ball so Doc was forced to play a 3 man rotation with Brown during crucial games during the playoffs. But early on we saw Cassell, Posey, Davis or Powe, and Brown getting in there, and I would think he had given TA a bit more playing time if he hadn't been injured right before the playoffs started. Davis and Powe were inconsistent so they were dropped off, and Cassell got replaced by House.
In 2007, it's a bit trickier because of all the injuries, but no doubt if we were full on, we'd see Garnett starting, and all of House, Marbury, TA, Powe, and Davis getting minutes early on.
But what we did see was Moore getting minutes early on until he exhausted his chances.
So in all, I just can't envision Doc not giving all these guys chances early on before he settles into a rotation, and given that most if not all of these guys are veterans, they should get plenty of chances. And if one isn't showing up, I don't think Doc would hesitate much to insert TA. So really I don't think we'll see much of short rotations in my opinion other than if a series takes a turn for the worse or in crucial games.
But yeah, I agree with your 8+ idea of those 1 or 2 extra guys coming afterward for shorter stints as needed (probably Finley and Baby in this case). Though I think Rondo will be seeing the most playing time so that might eat up into Nate's playing time.