4.
In some ways, it's easier to go from short form to long form than vice versa. I used to make 30 second 'movies,' and I think if I only did long form I would find it difficult to adjust to that short a length. 'I gotta say something in 30 seconds. Forget about it!' There have been directors who have done commercials over the years, but they seem to be the exception.
Joe Sedelmaier