Okay, 1 Andro is not going to aromatize, and you would have to be running 4Andro pretty high to need to worry about it being an issue...
An AI can definitely help in a PCT, especially if it is an OTC PCT, like for something like the andro runs if not too high. Lowering estrogen tells the pituitary to create more testosterone which results in LH and an increase in test. Someone running a SERM though, they really shouldn't need one, but they can be beneficial for stopping an estro rebound if someone was just running nolva or something for estro management on cycle. There are very specific uses, and people here about them and while applying the kitchen sink protocols add everything in.
I mean the supplement companies sold them on needing it and got everyone on the board to say they are needed for a reason. So they can make money... Selling fear of side effects, or lost gains will motivate a lot of people and the longer and more it is repeated the more it is accepted as fact that an AI should be in every cycle.
Meh... I think the fat under the pecs is more of a genetic thing. I have had that all of my life. Now it could be a genetic predisposition to high estrogen or estrogen sensitivity but I have it and all of the females in my family have huge breasts. I think it is just a propensity to store fat in that area... I would think DIM would probably make you feel healthier and with no other estro sides I wouldn't worry about managing it with an AI. You may not need it at all. A lot of people don't need an AI even running 500mg of Test a week.