How do you know what initial aperture to set?

Answer 1

It depends on what your shooting, you can also use AUTO mode on your camera to have your camera choose what aperture it thinks its best. If you have a high shutter speed than you might want to choose a bigger aperture (f/2 around there). But if you want a larger depth of field you need to choose a lower aperture (around f/32) and a lower shutter speed.