At the moment I expect the APC version to also be the 'dakka' version, with multiple assault and bolt cannons. I don't think there's really room for heavy AA as the very large hatch leaves little spare - the actual space available is comparable to a Baneblade otherwise. I also don't want to make the tank much taller - its already very tall compared to most Marine vehicles.
The tank should be quite capable against urban targets. Anything that can't be effectively destroyed by the array of assault cannons would likely be assaulted by jump pack or regular infantry carried aboard.
Flyers are trickier, but I don't know that a dedicated weapon system is necessary. I may add a radar scanner to the FW turret though.