Taking into account room dimensions and ambient light would be important for sorting out the flash lighting. I would agree that bouncing the flash off the ceiling or or using some other method to diffuse the light is going to be key. In a small room with light colored walls and ceiling the flash can bounce and soften nicely. In a big, open room with high ceilings it's a harder thing.
I would see about having the SB600 on another tripod or stand have it fire into a reflector or a nice bright white wall behind you. I've been known to use the built-in flash as a CLS Commander and have it fire the bigger unit that's aimed at the ceiling, out of line of the actual shot. This can give pleasing lighting without generating a lot of red eye.
What lens you should use depends on how close you end up. If you're fairly close, then the 50mm is probably perfect, since it offers a normal angle of view on an FX sensor.
This sort of thing can be fun if everyone is patient and having a good time. Otherwise it's like herding cats.