Most tents would be OK in winter if at low level & sheltered. could add some extra guys
Foam mat & SIM & good s/bag should be OK. Wear spare clothes inside, eg microfleece top, long johns & socks kept dry just for sleeping
Keep gas cartridges in the s/bag with you when not in use
Fill pan with water at night, then if it freezes you just have to put it on the stove in the morning
Keep water bags & bottles in the inner tent as it's slightly warmer. Store them upside down so that if they freeze the ice does not form a plug at the neck
Can use water bladders and bottles as hot water bottles as long as the water is not nearly boiling. In the morning you will have lukewarm water and be well on your way to your first brew
Pull a body warmer or fleece jacket over the bottom of your sleeping bag; besides extra insulation it will protect the bag from damp & condensation from rubbing against the tent walls
Take more fuel than usual, to allow for extra brews or melting snow, or simply because the water will be starting at a lower temperature
Besides your usual food & drink take extra hot snacks that can be cooked with the minimum of fuel, like instant noodles, cup-a-soup, frankfurter sausages. Yes, I know they're junk, but you don't have to live off them for ever
If you need to melt snow, either start very gently, or put some water in the pan - because snow will soak up its own meltwater at first, leaving the pan dry, and it will burn
If you leave your tent with the gear in it, always put the s/bag in a waterproof bag - especially if you think your tent is a bit suspect