Heavy vehicles now require tech before they can be called in:
Tiger, Elefant require Battle Phase 3 OR T3 building
Command Tank, Puma, Stug E requires Battle Phase 2
KV-1, KV-2, KV-8, IS-2, ISU-152, T34-85, Sherman require either T3 or T4 building.
Not sure about this one as you descibe it. Wouldnt this cost to much of mp and fuel meaning you seldom could afford to call in the call ins? You could build the buildings or tech up without building any tanks from it but would this actually help the meta in any way? If the call-ins require tech or buildnings you maybe have to make the call-ins a bit cheaper? Making them cheaper would make the commanders with call-ins much better than the commanders witout call- ins. Just some thoughts.