Welcome to the Winni Winter. It's especially beautiful up here during the winter and generally pretty safe as long as you wear your common sense helmet.
I know the following is a bit repetitious but since we have at least one or two serious accidents or fatalities a year it bears a fresh retelling.
The serious accidents involve these factors, mostly all at the same time.
1. Drunk - simply don't drink and ride
2. Inexperienced - stay on known, marked trails (get a trail map), don't explore alone especially at night, travel with others who know the area
3. Out at night - it's colder, harder to see, less people are around to help. Enjoy it but respect that it adds challenges to the ride.
4. Going too fast for visibility - don't outdrive your headlights, realize that the lake is NOT flat and that ice heaves and plow piles and such can be extremely hard to see (at all times) and very dangerous. If you feel the need for speed cruise the area slowly a few times to check it out.
5. On water - realize the lake is not at all consistent, frozen solid in one place and wide open in others, bubblers and currents can undermine ice. Is you get in trouble, speed is your friend - even keeping you on top of open water if need be. Keep distance between riders so one in trouble doesn't quickly become three in trouble. Consider flotation gear.
6. Crossing roads - cars always win, realize you may panic a car driver into doing something dumb. Give them a wide berth and approach roads slowly.
Signs of the lake ready to ride
Bob houses, usually pulled out by motorized vehicles and the fishermen drill ice holes and know when the ice is thick enough.
Don't rush it, the risk is not worth an extra weeks riding. If need be, trailer around the lake (ex. Castle parking area) and head up into the mountains.