If I am looking at quantity, I use 8x or you can use 10x depending on your scope. If I am looking at morphology of the sperm, I use 40x. Your eye piece is 10x magnification combined with your 8x objective lens makes this 80x. Hope this helps.
If I were looking for a microscope my "must haves" are a binocular,(2 eye pieces), and a light source. It's not mandatory, just makes viewing easier.