There's an old saying - "get into the best you can" Molly - so your pitch should have a couple of your top Unis and a couple for insurance if you don't make your grades.
Not considering Marine Bio at St Andrews then? That's supposed to be a hell of a job.
I would then think about distilling out the key factors that you are looking at in a course and weight them out of a 100 or 200 points to get at their respective importance to you. So that when you visit you can quietly grade each of the places. This should include not only the academics but residence, safety, social, sports, etc etc..........