depends on the state(s) you practice in. You'll have to do COMLEX 1, 2, and PE for graduation. After that all that's left is COMLEX 3.
For applying to ACGME residencies you really should take USMLE 1, maybe also 2. No evidence so far of places wanting the USMLE version of the PE.
Some state licensure boards require DOs to be licensed via COMLEX. Others allow either COMLEX or USMLE. Since you're already taking all but 1 COMLEX exam by the time you graduate medical school and you have no reason to take every one of the USMLE exams at that point, it would seem wise to just take COMLEX 3 and be done with it. That way you won't limit your state choices later on down the road.