For a private loan you don't need to file FAFSA however it would be incredibly foolish to get a private loan because you didn't file a FAFSA and pay a higher APR. With Federaly backed loan it is possible that some or all of your loan may be subsidized so it doesn't accumulate interest while in school. Also unless you have incredible credit your APR will be substantially higher with a private loan resulting in thousands of dollars worth of wasted interest.
Generally best method is to 1) File FAFSA 2) You get EFC (Estimated Family Contribution) 3) Meet w/ school financial aid department. 4) School will setup package of loans and/or grants. 5) IF AND ONLY IF you still need MORE money borrow with private loan (due to higher credit requirements and higher APR).
You don't need to be in school to file a FAFSA. When it asks you to list schools you can either leave it blank or select all the schools you are "thinking about". Entering school info simply allows school to access your FAFSA info and speeds up the process later. If you don't the school will have you fill out paperwork to release FAFSA info to the school
