I don't think HCGenerate can prevent shutdown, at best it will act like true HCG and help keep you primed for recovery.
A proper PCT would have a SERM, DAA, and some anti-estrogen.
300mg/week is 20% above the most aggressive TRT programs I've seen, so unless you have naturally low testosterone, I'm pretty sure it won't be an incredible boost for someone your age.
If your goals really are just to be leaner, there are compounds that can be ran for shorter times (cyp needs at least 10 weeks, better with 12 of injections) that are more tailored to that goal.
Injecting once a week is "ok" but is only "noob friendly" if you have trouble injecting yourself, it won't really change how the test affects you (positively or negatively).