Does Bound by Moonsilver prevent crewing?
Bound by Moonsilver does not prevent crewing. Bound by Moonsilver has the ability

Enchanted creature can't attack, block, or transform.

Crewing a vehicle is none of those things, so Bound by Moonsilver does not affect it.
Here are the rules for Crew:


702.121a Crew is an activated ability of Vehicle cards. “Crew N” means “Tap any number of untapped creatures you control with total power N or greater: This permanent becomes an artifact creature until end of turn.”

702.121b A creature “crews a Vehicle” when it’s tapped to pay the cost to activate a Vehicle’s crew ability.

702.121c If an effect states that a creature “can’t crew Vehicles,” that creature can’t be tapped to pay the crew cost of a Vehicle.



So, the only way to stop a creature from crewing a vehicle is either with an effect that specifically says so, like Revoke Privileges as doppelgreener mentioned, or by keeping it tapped with an effect like on Malfunction.