Becket-Lester-Buchholz is the front three. Assuming the Yankees finish with the best record and choose the eight day series, then the Sox get the seven day. This means that with a three man rotation, the G1 starter gets three days rest to start G4, and the G2 starter gets four days rest to start G5. I think you go with the three man rotation in the LDS.
If the Sox get to the ALCS, they could manage a three man rotation again if they're willing to go with the G1 starter on three days rest for G4. That's the only circumstance in which short rest would be required.
If they go with the 4 man for either series, I think it's too early to tell who the #4 is. Nobody is standing out right now. Wake is hurt, Dice-K hasn't come back yet, it's much too early to form a judgment on Byrd, and Tazawa has been unreliable and is the definition of inexperienced.