I think you will find several fans of the Trek FX series here. I ride a 7.2 WSD myself, and it's a joy and has gotten me more into cycling than I ever thought I'd be. I ride it mostly on roads but it handles nicely on gravel. No suspension or anything like that--my former ride was a cheapo old mountain bike with a front suspension, but I haven't missed it.

You mentioned Marin so I just want to mention that my boyfriend had Marin hybrid for a couple years. I believe it was an '05 model, towards the low end of their price range ($300-$400 USD). He weighs about what you do, and he had a fair amount of trouble with the wheels (thrown spokes on at least 3 occasions) and I seem to recall that the brakes didn't exactly inspire confidence. That was just one person's experience with one model a few years ago, so I'm not trying to sway you against Marin, but just to point out that the low end of their hybrid spectrum might not be ideal for your build.

As far as security, just invest in a good u-lock or two, make sure they're big enough to go through the frame and a wheel. You can also make your bike less desirable to thieves by adding stickers, paint, etc, anything to make it more identifiable and look less new. Check and see if your city has a bicycle registration program, which can sometimes be a deterrent and/or aid in recovery if it does ever get snatched. (i don't have any statistics on that sort of thing, but I know I've registered my bikes in the last 2 places I've lived and it at least makes me feel better )

That's about all I can offer... Welcome to TE, good luck and happy shopping!