Twice a week is a lot more frequent than necessary. And if you just start it without driving, you are doing more harm than good. Once every two months is OK if it stands in a place where the temperature and humidity is stable. But then you have to take it out for a drive long enough for the car to reach full operating temperature, I would say at least an hours drive. Remember to keep your gas tank full.
If the temp and humidity is unstable and unfavourable, once a month. Again, at least an hour.
Disconnect the negative battery terminal in the mean time. Recharge the battery before storage, especially if it's cold. If you didn't change filter and oil just prior to the storage, do it now. If the storage lasts for more than a year, change oil once a year at least. This is due to chemical prosses, not pollution and wear.