Can I go back to school after becoming a nurse?

There is no need to get an associates and then a BSN - it would be faster and more direct to get the BSN as your starting degree. Do your first two years of work at a community college and then transfer to a BSN program. You actually need to have work experience before applying to an NP program, so you would not be able to do it straight through if you wanted to. Most schools require at least one year of work as a nurse, but you will be more competitive if you have 2-3 years of experience.

You can just go for an AA and become an RN, however hospitals are really twisting the arms of RN's to get their BS.

Yes, you can do it that way; and you should have nursing experience for NP programs anyway.