Masteron is good stuff, i just ran it and I like it. I used 250mg/wk along with 250mg/wk of tren and 650mg of test. I chose to use masteron as it seems to provide good strength gains, is reported to beneficially interfere with negative estrogenic effects and I am reticent to run high doses of tren. Definitely noticed the hardening effect to some degree, especially around the delts but I have big delts and not alot of bodyfat.
Like was mentioned, some of the aesthetic benefits of certain compounds such as dryness, vascularity and, in the case of masteron, hardness may not be so noticible at higher bodyfat or lower doses.
If the idea is appealing you can run it alongside your test through the whole cycle, or, as I will attempt next, add it in after several weeks to overcome the myostatin expression to continue your gains. It seems to be the consensus that increasing dosage or adding/swapping compounds later in the cycle is a good idea for that reason. A word of caution though, it has been reported by some that higher doses of masteron (maybe >500mg/wk?) can cause too much hardness and result in some discomfort or cramping but I imagine thats individually based and I have no experience with big doses of it as of yet.
So far as AI's go, arimidex seems to be the best. .5mg EOD or as I like .25 mg ED. Aromasin is another choice but requires a higher dose and is best taken with food as fat increases bioavailability. The former will block estrogen conversion while the aromatase enzyme will remain whilst the latter kills the aromatase enzyme itself for a period of time. As such Arimidex is preferable on cycle but aromasin may be better during pct. We cannot discuss sources as a rule of the forum but you may have success in searching online for sites that offer 'research chemicals'.
As far as sore nips go, it would be ideal to use an AI with your cycle although I'm unsure of the protocol or necessity of using AI after with low TRT doses of test. Keep a SERM on hand, nolvadex being the best choice. Because you are TRT an actual pct is not necessary, but the nolvadex will help stop any nipple soreness as it gums up the receptor sites at the nipples themselves. I've never experiences actual gyno or visual swelling, but I have had tender nips in the form of swollen glands beneath the nipple, and nolvedex at 25mg a day for a couple days tends to clear it up. I'm not altogether suceptible to gyno, but the swelling of those glands occurs when I take multiple compounds that work in a similar fashion, with just these two you should be fine.