Congratulations on the C25K thing and on your 5K and 10K races. 
Regarding winter maintenance mode running, it all depends. Running 3 relatively easy 30 minute runs will certainly do it for you, however, I've also worked out "only" three times per week and pushed pace and/or distance and actually made improvements. With that said, I suppose an argument can be made which says only two runs per week at say 40-50 minutes would bring the same results.
FWIW, I live in New Hampshire and we get lots of snow and ice, needless to say, I've had to learn how to safely run in the stuff. The following are two products I've used in the past to help with traction when things get icy:
- http://www.roadrunnersports.com/rrs/products/YKT100/yaktrax-pro-icesnow-traction/
- http://www.roadrunnersports.com/rrs/products/YKT102/yaktrax-run/
Keep us posted on your progress.