21 miles each way. I live in the alps, so it's a hilly 21 miles.

1. Last year, it was 5 days/week. This year, 4 days since I work from home part time. However, I have the option to take a train part way when the weather is really nasty or if I have to rush home.
2. Yes
3. In summer, about 1:15 to 1:30. In winter, 1:30 to 2:00. If I take the train part way, it's 1:15 (i.e. same as my fastest riding time). My riding time depends on the weather and how I'm feeling physically.
4. 5 bikes, but 2 are used mainly for commuting. The winter/rain bike is a 1999 Cannondale T700 (touring). The summer/good weather bike is a Trek 7.7FX ("road" hybrid). I also have a 2010 Crosscheck which I built with 105 components and DT Swiss R1800 wheels. I commute with the CC on nice summer days, but it's largely my weekend bike. Of the other two, one is a folder and the other a mountain bike. I've commuted on them too, but only on a few occasions. To haul my stuff, I use a trunk bag mostly, and panniers occasionally. Dinotte lights in front, superflash in back.