Lots of good advice above. I'm a big guy just like you, and I have yet to fall this winter. I roll on 26x2.1 Kenda Small Block 8s dropped to about 15 psi and they do surprisingly well. Just have to watch it when cornering or else the bike will slip out from under you, especially on snow covered roads where there's likely ice underneath.
That said, don't expect to have a particularly easy or rapid ride, what with the snow gear, low tire pressure and extra rolling resistance. The farthest I've done in snow thus far is right around the 11 mile mark, and it feels like I'm exerting myself equivalent to a 30 or so mile ride on my road bike while going a fraction of the speed. Wicked fun though!