Generally, your studs should be spread out evenly across the sole of your boot, with a slightly higher concentration of studs on the outer edges. Additionally, your heels and ball of feet make the most contact with the ground, so each of those areas should be well studded.
Whatever you do, don’t install so many studs that you replace your rubber sole with steel that’ll make your boots more slippery than having no studs at all!. Most purpose-built wading boot studs come in packages of 20, so if you want to be fully kitted out, you’ll have to buy two one package for each boot. Screw the Studs In But Don’t Over-Tighten hand tighten only don't use a drill if yoy over tighten the studs they will pull out in a short time.