best advice for a beginner is....
...DONT OVER THINK IT. A LBS will fit you to a bike that will hold your weight, if anything goes bad bring it back to them, they fix it. no matter what bike you buy now, n+1 kicks in quick
second best advice for a beginner is....
.....just get out there a ride and don't forget to say weeeeeeeeeeeeeee weeeeeeeee when going downhill.
I personally went cheap and got a $75 wally world beach cruiser (still use it to commute to work), but it turned out i like road bikes so now i have 2 road bikes and the wally world tank. I lost 40 lbs last year (would be more if running knee injury didnt happen).