Epistane is a methylated version of Epitiostanol; it is not a test booster, it is in fact a steroid albeit a mild one. Suprisingly you can find it at some supplements stores.
It is reported to have anti-estrogenic effects and as such is supposed to provide 'dry' gains. This is where your achy joints come from. In fact, epitiostanol combats the binding of estradiol to certain receptors. That being said, everyone reacts differently, and gyno can occur whenever you meddle with your hormones.
Yes you should do post cycle. Again, yes you should do post cycle.
I dont know what LGI-post cycle is, but if it contains nolvadex or clomid (doubtful) then it should be ok.
Nolvadex is typically preferable, at 40/40/20/20 mg a day for 4 weeks, supposing your 'cycle' lasted 8+ weeks (you in fact shouldn't use orals for more than 4-6 weeks as methylated anything is not good for your liver and alters your lipid profile). If it was less you can drop a week off. The Nolva should take care of your nipple problem if it isnt too severe.
Listening to a random friends advice is a common way to get yourself into trouble, always research what you are taking if are unfamiliar with it.