1) Can I apply for a private loan just to see what rate I get, and then if I don't want to take it, can I decline the loan?Bears did this with citigroup law loan. It was very easy, and bears were happy with the results. Be careful though, because if you make too many credit inquiries in a short time span, it can have a short-term negative effect on your credit rating.
2) Should I be applying for any loans now, or should I wait till next month or so? You can do it now or later. I like to have this kind of annoying stuff out of my hair so I can go back to swimming in streams and stealing hunny from bees.
3) Do I need to apply for Stafford before I apply for GradPLUS or private? Nope!