I'm a beginner at both. I'm finding that skate is much more intense - I can barely regulate my HR - either i'm standing still or at 95% max. Classics are much easier to go at a moderate rate. I've been skating for 1-2 hours (until I'm dead) and then I can classic for another couple hours after that.
You should definitely find out how hilly your local ski area is - if it's really hilly (mine is) skate is really really hard as a beginner. Classic is easier for hills - and you get plenty of workout.
My friend races both skate & bike, and trains separately for both. I think the real benefit is keeping your cardio up during the snow season, as opposed to actually building muscles that work for both. Someone please correct me if i'm wrong here.
Sorry to not answer your actual question.
And -1000 about Craigslist for skate skis - I would go to a real nordic store to get a recommendation, there's this complicated "flex" thing, and I think you can really make a lot of mistakes with your gear if you don't get some help the first time. It's not as simple as weight/height.
I did both today, it was fun.