Question about grafts

[Dav7]

Simple question concerning grafts. I've been reading that the number of grafts the average person has ranges from 4,000 (low) to 6,000 (average) and 7,000+ (high)............I think I have it right there. I'm just wondering if those 4,000-7,000 grafts are what we are limited to over a lifetime? And if not,

(a) how many grafts can re-grow

(b) how long do they take to regrow?

Also,

(c) Also with procedures with histogen etc. will graft count become irrelevant (even if down to only a few hundred grafts)...........or will graft count still be important and necessary for any future treatments such as histogen?