I'm starting PN at Mohawk this January. I considered the options the same way as you did- either way, it was going to be 5 years. So my reasoning was that if I do the PN course, and decide that I can hack 3 more years of school- then the option is open to me. If after 2 years I've had enough (I'm also a mature student, but I have a family with 2 young sons) then at least I have something completed that I can go out and work with. This might be something to consider for you, because I think some people work as PN's while they finish the PN-> BScN bridging course. The money is also a consideration- the BScN program is considerably more than the PN program. I'm not sure how the two routes stack up overall- that would be an interesting comparison.
I'm sure you're right about the May start for PN being a little less competitive- I think they get many more applications for the September starts. Mohawk only has September and January starts, and they are 16 continuous months with short breaks between the 4 semesters. Not to say that it will be easy no matter when you apply- the rumour was that they had over 1000 applicants to the January 2012 start, and I think they take about 80.
From what I've heard, Pre-Health is a solid way to get yourself into the BScN program, as long as your grades are up to snuff, but I'm not sure what the criteria are for getting in. I was accepted to that program too (I applied in case my PN application was rejected). I really don't know anything about the admission process for the PN->BScN bridge program, so I can't comment on that.
I hope that helps a bit! Oh, and.....