My thinking is that Moore will (and should) take time from BBD. Gives us a tall guy with a legit jump shot and he would definetely be an upgrade. I think Powe is basically a better player than both BBD and Moore and thus his minutes should not be affected much.
As for Marbury, he will fill in TA role and I think, will play a lot along side of House a lot. That tandem would be incredibly effective I think. Marbury should have much of a problem guarding two guards that don't start in this league. If you look at LA, they have Sasha which shouldn't be an issue. Cle has a bunch of guards in the 6' to 6'2" range and Marbury matches up with them as well. This of course will free up House to do what he does best, which is shoot.
Marbury also gives us insurance in case Rondo is being squeezed on the offensive end and the end of games. On this point, Rondo will have to man up and understand that in some case, it will be in our best interest to have Marbury on the court. I don't see any potential for long term resentment since everyone knows that Marbury has no future on the Celts beyind this year.
Bottom line: I think we these two additions, we are now rock solid. It will be up to Doc to make it work.