Although the SM codex specifies that the MotF can take servitor(s), it does not mention them being a retinue for him. In addition, he is an IC and SC, not a standard techmarine. Therefore, I believe one or more servitors would use up an elite slot in your list as the MotF would technically be joining them. EDIT: SM FAQ Q138 says servitors don't count against FOC.
Remember that vehicles don't get cover saves from being in area terrain per se (BRB pg 62). If they are >=50% obscured by a piece of terrain that confers a 3+ save to infantry, then the vehicle gets the 3+ save (unless otherwise modified by the rule exceptions).