as said earlier, you can add primo, but only if you know what you're doing, why you use it and so on. since you never cruised before, start with test alone. maybe later you'll add primo. as for answering your question, it is becuse you are meant to recover from a cycle. the more steroids (and higher doses) the less you recover from the cycle. primo is mild, but it doesn't mean that it can't have side effects or negativ effects on your health.
no, if testicles are in normal size and you do not really want to have children, no need for HCG. but if you do want to have children in the future, check sperm quality/quantity every once in a while (even if testicles are normal size).
normal range 163 to 517 ng/dL? wtf? normal T levels for pussies? it is 300 (which is likely too low) up to 1000 ng/dL. your 1300 ng/dL is fine for a cycle (many try to get higher numbers particularly when bulking) but slightly too high for cruising.