lol... lots of variables there. Most of us start off with solo cups, move up to 1 or 2 gallon and then up to 3 or 5 or 7 or 10 gallon containers. The number that you can fit in your 4x4 will depend on that final size. I find 6 plants at the 7 gallon size is about right for me, but 4 might be easier. If all your plants are only 3 gallon, you could probably get 12 of them in there without much trouble.
Sounds like you need to do a lot of reading. Start off looking at beginner grow logs and try to learn by watching these other new people making mistakes and learning from them. Read everything you can on growing these weeds, start up a grow log so we can help you as you go along, and dive right in! No one is an expert at first, so set your expectations realistically and see what you can do! I guarantee that you will learn a lot during your first grow! Good luck, and know that a lot of fine people are here ready to help you when and if you get into trouble.