This is my take on how much of an AI to take, incidentally each and everyone of us are going to react differently as our endocrine system are not identical to one another, it becomes very individualized to dictate what is ideally correct or balanced when using an AI.
The standard amount of 6.25~12.5 or 25mg ED, EOD,E3D are common protocols with Aromasin, how much though can be easily measured by nocturnal and morning erections.
Assuming you have no previous issues with libido or maintaining an erection? Start of with the lowest dose on a daily basis, if you notice that you maintain a nocturnal and morning erection on said dose, your dialed in at a proper E2 to T ratio.
Estrogen is needed for proper erection/sexual function.
If your after water retention loss, an AI works wonders to aid in this, as diet also (as if you didn't know that).
Something to consider is running a low dose of T3 along side of your cycle, you'll notice a little less bloat.