Hi Olivier , that sounds like a great idea to do two sets of crews. I would go along with Ken's suggestions regarding pose and shell's etc.
Just on that not "If" you do make the shells , can you ensure that they are the Pak 40 type... long skinny one and not the shorted KwK 40 round?
Photo link one shows the Pak 40 type.
Photo link two is the KwK 40 round as used in the Panzers IV G-J/ Jagdpanzer IV etc.
Best regards
Paul