You can put any combination of 2 Nova's, Ballista's, Centurion, or Spartan's in either a M2 (recommended) or C2. You can only pick 1 in the A2, but it has other uses. The Storm looks big enough to take up 1 of the cargo grids too, so it can probably be added to the list of vehicles.
Yes, you can overload these ships, though it's not always a good idea. We have spent hours fixing the mess that not understanding how the cargo grid works can cause. Hint: Multiple crew with Multitools come in very handy if you want to overload the ship, and then be able to get everything off the ship later.