Nah man, they're not ridiculous at all.
I did the HHMI year-long fellowship last year (07/12-06/13). The application for the fellowship was due for me on January 11, 2012. I began looking for a mentor in August 2011 and found one at the end of August. We met several times between September and December to talk about the project, and we wrote the proposal (5 pages) between November and January.
It doesn't hurt to start looking for mentors as soon as possible--especially because you'll probably be busy doing other med student stuff during the year! I'm not sure how many PI's to ask, but do your homework when searching for a mentor--look at their papers, talk to med students who have worked in their labs, and talk to trusted professors at your school who can point you to good mentors. I think it is also important to make sure that your future mentor has strong funding; you can check out this site (
http://projectreporter.nih.gov/reporter.cfm) to see who at your institution has NIH funding, and can even look up research topics that are of interest to you. I never had a problem getting in contact with potential mentors through e-mail, but of course I would always try to set up face-to-face meetings.
I don't think med school ranking matters much to HHMI, more so the research potential of the student, track-record of the mentor, and the quality of the proposal.
