What's confusing is that even if I delete or neutralize the validateRequiredFields(), your code doesn't have any validating functionality whatsoever -- if I enter nothing and click 'Submit', nothing happens except the page returning to its top position. So you should really come up with a code that is basically functional, and then ask for additional or more specific functionality.
One question I can already answer, and that is that you can have as many IDs as you like, as long as they are all different. You cannot have multiple identical IDs.
Regarding Sitepoint not offering the right tutorials for beginners, I would agree with that. But it is primarily a forum. Also, it seems to me that you dove off the deep end, and are now asking for help so as not to drown. That we do the entire debugging or code completion for you. I could imagine wiser strategies, such as starting with a simple internet search for form validation tutorial or 'how to'.