I would suggest that you always use an AI on cycle from the start and not wait until there is a problem. Any of the AI's will work but dosing will be different for each and dosing will be differnt for each individual. For instance, I find that I need much more arom than some people. My suggestion would go with arimidex. For 500mg Test EW, I would start with .5mg EOD and if you find that you still have an issue, I would then increase to 1mg EOD.
I would also split your weekly test dose up into 2 smaller shots instead of one large bolus. This will keep your test levels more consistent and less likely to cause side effects like gyno. I would make sure that your estrogen is under control before you start adding Tren, espeically tren e. Technically, an AI will not stop tren from causing issues. Now, if your estogen is under control, it will be less likely that proges will be a problem, but proges and prolactin levels will not be directly effected by an AI. If you find that you can control estrogen with your AI, but still have issues with tren, you might want to look at caber, .5mg 2x wk