A nice aero rim gives alot of strength for big guys. As long as you get something thats pretty 'bombproof' and get it 36 holes laced 3 cross with fatty spokes you should be golden. I'd forgoe the 27" wheels because they're pretty rare these days and you can find much more quality, strong, light and cheap rims in 700c. Maybe something designed for tandem use would be your ticket.
As for the 175 cranks, thats up to you but it depends what kind of riding you are doing. If you like to do touring without that much turning you'll be fine, but if you're doing city riding I wouldn't reccomend anything more than 170 really... you'd be asking for pedal strikes and they're not fun. Look for a frame with a nice high bottom bracket and that should counter any loss in height from shorter cranks and smaller wheels