So buying a snowboard?

You'll probably want a board closer towards 150, a 140 is pretty small for someone that tall. It might take a little to get used to but it will be better in the end. As far as styles, shapes, sidecuts and flex go, the only thing you will notice is flex which is how soft the board is. Side cut just means how thick the boards edge is basically, the thicker it is it'll help with turns but seeing as you're a beginner it doesn't matter too much. For girl boards I'd say roxy is probably one of the better brands they have magna traction now which is more contact points on the edges to help you turn. Try looking at dogfunk.com they normally have really good prices.