All of them.
The Fuser won't overheat, it will heat up and cool down throughout the job (pages will come out slower during cooldown phases)
Nobody can give you a number because it will differ by job and stock (A page of solid coverage needs way more heat than a page with a small letter D in the center and no other content)
Hy,i have a xerox 4510 printer and i wold like to know how many pages can i print continuosly without overheating the fuser.