Requires at least 2v2+ and another USF player. Cache + Mechanized withdraw ability would make you able to get a Stuart by 5mins if you also use the Captain ability of supervise.
Only thing they need to do with crews, is fixing/balancing repair crit.
-Increase cost
-Fixing it so it actually requires the "whatever time it needs to repair instead of 0.5s"
-Not removing heavy crits completely (for example an immobilization goes to heavy/light engine damage. You can then repair crit again to fix it completely)
Fuel cost and timing. You want an M5 as fast as possible, so once you have enough fuel for T3, you should built it as the time it takes to build would be enough for you to collect fuel for the halftrack.