In the museum, is it like at Aberdeen Tank Museum, where you can climb onto and enter the tanks and vehicles, and pose in them for photos, etc.?

thee is no climbing on the tanks . Aberdeen does not allow it also the insurance will not allow climbing also

No such opportunity to climb into any tank. There is a prop tank at the north east corner but not even that one has any improvise photo ops.

No, most of the vehicles cannot be climbed on. There is a self paced tour ( using a guide book) along a well marked path. The curator is often a available for questions .