a lot is at the very least id think, 200. ideally 2000+ for any statistical data.
i did 50 Nihlathak runs. got 1 key. felt terrible, but not enough to draw any conclusions.
I can tell you ive done well over 200 runs. If I had to guess - around 1000 runs so far between nith/summ/count.
I have 15 keys total.