I'd pump up the tires to 45-50psi - I 've never actually HAD a problem with flat-spotting, but I do this routinely, as winters here are LOOOONG, and I wouldn't want to find out the hard way.
I also disagree with the idea of starting your car periodically throughout the cold months. The vast, vast majority of wear on an engine occurs when you are cranking it to start. Why would you subject your engine to wear that you don't really need to? The idea of doing it to avoid rubber getting hard is very much passé - you will do more harm than good, here - I frequently hear of doing this to "prevent dry rot" of rubber hoses - this is the 21st century. There is NO empirical evidence to warrant regular starting of your car. The car will never get properly lubricated or burn off the condensation formed during short idle periods that way.
Here's my winter storage regime
-Full tank of gas, add fuel stabilizer - run engine for 10 minutes to disperse stabilizer throughout fuel lines
-Tires inflated to 45-50 psi (I really do think this is unnecessary, however - one year, I forgot to do this with a BMW M3, and had NO problems whatsoever).
-Parking brake OFF
-Full detail prior to storage - wash, claybar, wash, swirl mark removal, wash, Zaino Z2/Z16/Z2/Z18. Treat leather surfaces thoroughly - leather cleaner, followed by Zaino leather conditioner. (Leatherique, if it older leather in need of restoration)
-Treat all rubber seals (windows, trunk, etc) with Aerospace 303 protectant.
-Change oil if it's anywhere near needing it.
-Temperature controlled garage.
-Lower the windows about 1/4", to avoid rubber "memory" (I used to also put small blocks under the windshield wipers, with a similar idea).
-Indoor car cover - but NEVER put any car cover on unless the car is completely dry.
-Battery tender - NOT a trickle charger.
-Shed a tear, and begin dreaming already of next year's driving season
I think that's about it.
Sometimes I REEEEEALLY envy the guys and girls that can drive year-round......
