That's hard to say yes or no to definitively as it varies individual to individual. Your hair characteristics are a factor, how viable your donor is is a factor, what level of progression your headed toward and of course your expectations. I've found in general that guys with extreme loss are the easiest patients because they are happy with virtually any improvement that makes them not totally bald even if it's not dense or perfect but a guy with some minor temple recession who is a nw 3, he may put as many grafts into his hairline alone as that nw 6 guy did on his entire scalp chasing natural density and go thru multiple ops chasing that. If you're a nw 4 and under where the crown loss isn't severe and you're realistic you should probably get thru your life on transplants alone even without meds, more likely if you have good hair characteristics or a strong donor ...if you're a nw 5 or have thinner hair or just an average donor you may have to compromise on getting ideal density everywhere, most likely live with just coverage on the crown... maybe not getting the density you have up front but you could get thru, this is the range it gets dicey unless your donors working for you. Nw 6 unlikely you should be looking at fut. Nw 5 may even be better off looking at fut unless your donor is strong and the hair characteristics are working in your favor.
Overharvesting and noticeable extraction patterns are concerns with fue but in the hands of top docs the numbers retrievable has gone up significantly. The procedure has evolved and the tools used improved to the point that transection rates are close to fut transection rates, the punches used minimize scarring and the emphasis on donor mapping to make sure noticeable extraction patterns don't emerge has really pushed the procedure forward and what was thought to be the upper level of available grafts in the past is now considered below average. The euros really took the lead on fue and the numbers they're able to extract are incredible. I've seen a few cases of 10k + extractions where the donors still look immaculate and untouched. Even as short as 5 years ago, getting 6k was considered amazing, now it's routine. 2 of the leaders in fue in Europe are my own doc Lorenzo and Dr Erdogan from Turkey and they came up with the coverage value system where they effectively map the donor and have come up with a formula using your hair characteristics to determine how many grafts can be taken before the loss is visible to the human eye. I've had my own scalp measured and my available donors is near 12k left and I've had 4k taken already. My donor is way above average strong, the top American docs had me pegged for 10k available fue grafts they just couldn't pin down how much over that they could go, they eyeball it where the cv system was supposed to take the guess work out of it. Few people have pushed the limits of what the coverage value system says can be taken but I've seen lots of cases where they will dip into 75% of that limit successfully but few people need to dig past that amount. How many a doc can get will vary given your donor and your hair characteristics but if you're starting to get peak thru in the donor after 4k the doctor wasn't very good or your donor wasn't...an average donor these days should yield you comfortably 6k...a solid donor 8k+...and a good donor 10k+ and these are fue numbers.
For example here's a dr Lorenzo patient, they have his coverage value info up at 44 seconds but it's a little tough to read but they mention his stats under the video...and the patient pre the first op, it was a 2 stage op, had nearly 13k grafts available, after 2 ops and 5100 grafts taken you can't see any noticeable harvesting issues
https://www.youtube.com/watch?v=RT76HJ8mkt0
then this vid, this patients nearly 9k grafts in over 4 procedures and he's young still just 37, virtually all his hair is transplanted hair at this stage so he doesn't have the fear of going thru further major loss, he was lucky to have a strong donor but you can see 9k grafts in the donor looks pristine.
https://www.youtube.com/watch?v=DdEMMSdmlQg
So there is no set number on how many grafts or how many procedures in before the donor will look weak it depends on your personal factors and the greats will take those into account and plan accordingly.