As many as it takes.
You can still work in your 3 zones, tip, stress,cuticle, but it may take more than one bead of products in each zone on a very long nail.
Ideally you would just pick up larger beads though and still use 1 per zone.
1 bead method is so helpful in cases of long nails. The best way to do it, IMO is start at zone 3 and work your way up. You use your normal size beads and apply how you normally would with short enhancement up until you get to zone 1. Since the tips are longer than usual, you can use bigger beads and cover more area quicker and neater, placing the ball in the middle and feathering to the sides. This both builds a "spine" and if your application was neat and seamless, would require minimum filing to finish off.