Note: There is no need for the scissors
I used an old bra and about 80 pyramid-shaped studs, but it depends on the size of the studs; for example mine studs are about 8 mm.
I think that for this kind of diy is better using a balconette bra and pyramid studs, but it's up to you.
I used studs as shown in the above image, in italian we say studs with "alette", that means they don't have to be screw on, but you just close back when you apply the stud it to the bra.
I didn't use scissors to make the holes. I just applied the stud, by pressing the "alette" (the pointing bit at the back) to make the hole. Then i used the pliers to press down the "alette" and so the stud is fixed in place. Then you repeat this procedure for every stud, until you finish your desired design.