Is there a limit to how many units any air craft carriers or transports can take?
Air Craft Carriers can carry 2 planes (Tactical Bombers or Fighters, Strategic Bombers cannot land on carriers. So the possible combinations are 2 fighters, 2 Tac Bombers, or 1 Fighter and 1 Tac Bomber). Transports can carry any 1 land unit + an infantry (so 1 infantry + tank, 1 infantry + artillery, 2 infantry, etc.)
Your basic strategy is correct (there really isn’t much Russia can do in this game but delay the inevitable and save as many troops as possible for Moscow), though I’d emphasize the UK’s immediate priority is dissuading a Sea Lion attack (easy) and establishing Naval supremacy in the Med (usually not that hard after the Taranto Raid).
I would also heavily recommend taking S. France on Germany’s first turn and looking to help the Italians in the Med. In order to win as the Axis, you need 8 Victory cities, which means you have to take either Cairo or London, and the easiest time to take these are early game before the America come’s barreling in. It’s tricky, but this game definitely isn’t friendly to the Axis powers.