Use what you need to and dont worry so much about what the quantity and you will find as you become more experienced that you will use a lot less..
Also depends on the type of wax you use, how thickly you apply etc... I use two types of strip wax and find that the cream based ones uses more strips than the other one.
Also IMO I find the thinner the strip the better for picking up and I use less. I use the extra thin strips from Salons Direct , try both thickness and see which one you prefer.
Good luck and hope it all goes okay