Mobile Garrison

For a Vehicle to be able to attack, it must be a creature as the declare attackers step begins, so the latest you can activate its crew ability to attack with it is during the beginning of combat step. For a Vehicle to be able to block, it must be a creature as the declare blockers step begins, so the latest you can activate its crew ability to block with it is during the declare attackers step. In either case, players may take actions after the crew ability resolves but before the Vehicle has been declared as an attacking or blocking creature.

If a permanent becomes a copy of a Vehicle, the copy won't be a creature, even if the Vehicle it's copying has become an artifact creature.

Any untapped creature you control can be tapped to pay a crew cost, even one that just came under your control.