Just fill everything out as soon as possible, but don't get all anxious and don't decide not to file.
The FAFSA is the most critical because it takes weeks for the data to filter through to the school's (often antiquated) processing systems.
One school I spoke with said that they required parental data on the federal FAFSA (even if independent) because there was no other way to get the info into their computer.
Remember this isn't finaid for all of medical school, it's just for the first year. Even if things go badly for you this year, you will apply next year (and the next, and the next.)
In fact, if you spent 2003 working at an FT job, you may find that you are ineligible for anything but federal loans. You might not need to gather all your parents' money secrets in this case. Most finaid departments will tell you to apply anyway, just in case some miracle happens and the rest of your class spent 2003 working on Wall Street or something.