All dependant on size of space and size plant you want. Heres a current scrog pic if it helps you visually
This plant is in a screen I made with about 1.5"x1.5" squares. The screen itself is 2'x3'. Had a time crunch so flipped early before she filled up the screen. She is about 2'x2.5' give or take. Id say about 60-70 tops all together. I feel shes crowded though but growing been just fine so far.
Its pretty much going to depend on how long you want to Veg. Give some environment conditions and what medium your growing. Strain and also nutes your using. As accurate as you can be and alot of us can try to figure an estimate size of plant per weeks in veg. Do you know how long you want to veg?
Or just build a big screen and if it doesnt fill, it doesnt fill. But per plant 2'x2' is a good size for small spaces. Bigger plants can fill a 4'x4' screen easily. Just remeber to give yourself working space around and underneath your plants