You can use HCG whenever you want before,after, durring, or in another lifetime but the smartest way to go about it is to use it durring cycle from the start so your testicles never completely shut down. That is the best method whether you are using tren/test/dbol/deca whatever...at the end of the day being shut down is being shut down, I would prefer to have my testicles functioning the whole time rather than letting them die and hopefully come back to full strength when I randomly use HCG before PCT.
Your body fat % is for sure too high to cycle in my opinion some might disagree, and it's 100% without a doubt too high if you aren't going to use an AI throughout the entire cycle. Higher bodyfat% = more aromatization and that means more estrogen and that means more side effects and gyno. It's tuff to manage e2 even with an AI when you are overweight.
Deciding to increase or decrease the dose is very common.... but not after you have started the cycle. You want to avoid hormone flucuations and get to steady levels as fast as possible. Switching things up causes problems. Your dose of tren is wayy to high, especially since it is your first time using it...you don't need that much unless you are a professional bodybuilder or male model making money off of your body, which i doubt you are
I'm not trying to be a jerk, just trying to point you in the right direction
Good luck