Good luck with the road traveling. You'll need it. As much as it sucks to load up your car and drive the 2-3 miles to Lynn woods I would strongly suggest it. There is just no nice way to get from Lynn beach to Lynn woods. I lived on Wave St. for a few years and would always just make the drive instead.
And... most trail bikes will survive riding Lynn once in a while but if you really get into it and ride there a couple times a week they will start to break in my opinion. It all depends what you want to do there; if you always take the b-line most anything with 4 inches of travel will be fine, but if you know you're the type of person who will start riding harder/bigger lines you'll want a burlier bike.
AM hardtails are fun for Lynn but beat the shit out of you. And as I found out recently, when switching to a FS, are not an advantage going uphill unless you have mad trials skills (which I don't).
Bikes..... Specialized enduro, pivot firebird, Santa Cruz nomad, and most other bikes in the category that I'm forgetting.