Getting a proper DM would properly b d best decision... You would have your usual 3 man MF with Masch or Busi as lone DM. If Xavi is to be rested play Masch as DM, Busi/Keiteee as BTB & Iniesta as primary play-maker. If Iniesta to be rested play Messi as AM(he has been really impressive in WC in that role) or Keiteee or give chances to youngsters.
Its all fine we would have numerous options, but the problem is that the Don is too injury prone; we had same options with Yaya too and Pep never seemed to be willing to go for them(the 1 or 2 times he did he was forced to, as Xavi was out injured and he had no other option available!!) You would think Xavi will b able to get some rest with so many options at his disposal but I seriously doubt Pep would risk not playing him, even against minnows!!