Winter Cycling

Hello folks, I've been off the forum for a number of years with adding a few kids to the family and going back to school. I'd like to say I'm done with that whole deal but kids are a lifetime investment and the books just keep calling me back. Either way between changing diapers and dodging heavy books I've found time to re-focus on endurance sports a bit, and I've come up with some questions.

Winter cycling, do many still cycle outdoors once the snow hits or do you start heading to spin classes?

If you stay outdoors do you keep with your road bike or move to something more mountain bike geared for grip and gear ratio?

Tips on layering, body heat management, goggle fogging?

Also - I hang my hat in Ottawa Ontario.