I use all natural coco-naras and for poking holes i generally do about 20 holes (diameter of my bowl is about 2.5 inches) and i put less holes towards the center of the bowl since it receives more heat especially with 2 coals to avoid burning the center.
General rule of thumb though:
the more holes: the hotter the coals will get when your inhaling aka more smoke
with less holes: harder for the shisha to become harsh, longer lasting bowl, less smoke
It's really all preference though