One other thing to keep in mind with the Aztecs. The Tarascans and Thraxs have the exact same line-up that you do. The Mayans have mostly the same units you do. The Spain use different units, but there's are mostly superior to yours...as a result, you're not only surrounded by enemies, but you've got a serious "Anything you can do, they can do better" problem.

Simply put, you can't realistically overpower your enemies with elite units, or out tech them, or anything of that nature. Since you're on level ground (at best) with all the enemies you'll be fighting most of the campaign, winning battles is pure numbers, tatics, and campaign map positioning. With no Cavalry and an army based mostly on heavy infantry, there's only so much you can do to overcome superior numbers, so don't get reckless in tackling 3 enemy stacks at once. You aren't the spanish, and even a full stack of Jaguar Warriors can get torn apart quickly when surrounded by hordes of cheap spearmen and archers.

Also, no Siege Weapons combined with the above means that offensive sieges are a pain in the arse. Unless you have overwhelming superiority, you'll often have little choice but to wait them out, as even rebel settlements are usually defended by 12-15 units.