Check out the 'About the Pharma' thread at the top of the board, there are some good bookmarked threads in there with answers to a lot of this.
If you take the aromasin during cycle, you won't need it during PCT. Aromasin kills off the estrogen (suicidal AI), while arimidex and others merely block the estrogen from binding to the receptor. If you are taking one of those type AIs, then you have to worry about estro rebound because they do nothing to lower the amount of estrogen in your system. If you take aromasin during cycle, then there is no estrogen left to rebound when you come off - your body is starting from normal levels (and yes, you still want some estrogen to be able to function properly). Which AI did you take during your cycle?
It is my understanding that you don't need an AI during PCT - it won't be detrimental necessarily (someone chime and correct me if I'm wrong) - but there is no benefit. At that point, the SERM is taking care of any estrogen in your system (as far as blocking conversion or binding) while also stimulating LHRH and FSH to get your natural production started back up. Honestly, I am going from memory on this, and I don't worry about PCT anyway since I am currently blasting and cruising (TRT when off cycle). Check in the 'About the Pharma' thread like I mentioned, there are a couple bookmarked threads specifically dealing with PCT and which drugs do what - look for stuff by KSman, he seems to be the authority on TRT and PCT related stuff around here.
As to the HCG, that one is up for debate. I know guys who rarely (if ever) use it and have no issues restarting, while other guys swear it is essential. A far as which drugs affect what, I've never heard of a tren or deca cycle requiring HCG while a test only cycle does not. Most of what I've read on it is all or nothing.