OK: here I go again! I really hope someone more expert may write here to confirm or deny my observations; it seems you can create FMB to plan a mission on any map using ONLY German for Blue and Russian for Red aircraft in all the flights for Squadron 1: these can be selected and modified for type/air force from QMBP menu.
Any other Squadron can belong to any Air Force and be composed of any type of aircraft, so you should take care to have them coherent with the period/mission you have in mind, since these other Squadrons will always be present in the mission and cannot be disabled from QMBP menus.
As for vehicles and static aircraft, I noticed with my dismay (it's a bit of a let down!) in many missions included in the QMBP download, they have been assigned to USSR or Germany only: so you take off from Luqa in Malta, and all the planes around are Russian Yaks, Laggs, etc. It would be just a matter to change their properties/types in FMB, and this operation doesn't seem to create any trouble: if anyone has a better understanding about these ideas, I would be grateful to read it here!
Thanks for reading.