well dude, this is just my opinion, and it varies by riding style, preference etc, but I'd definitely say stick with the 158. The 156 seems a bit short for you and as you progress, you'll be thankful for the extra length when going at speed.
I don't think you necessarily need a wide, although I think you are borderline. It sucks, but it really is best to go down to your local shop and see how everything fits. Its a bit uncool, but you might consider going over to SkiChalet off 270 in Gaithersburg and seeing how things fit then buying online. Like I said, its kinda uncool, but hey.
Also, yeah, craigslist works, but also check out discount sites like sierrasnowboard.com and backcountry outlet. If you're not picky, you can find good deals on there. If you're trying to go REAL cheap there is a place called the baltimore ski warehouse. They sell both used and new stuff, but you could walk out of there with a whole set up for like $100. Just can't be picky . . .
again man, just my thoughts