"Then if I make more, give them a percentage?"
That's the deal on tapes Gaping Hole releases. % of the original batch then more artist copies if he does another run. So far, I don't think another batch of the MANIA tape has been made. First 100 probably never sold out though I should inquire...
I would think for most PE/HN tapes, 100 is enough & for most vinyl, 200-300 is more than enough. Someone like Genocide Organ could easily do 1000 LPs & sell out maybe a couple of months later than just pressing 500. I can't imagine even Prurient selling out more than 1000 Lps & copies being very hard to find.