The answer for you is probably going to be some combination of all of the above depending on your situation, so let's go through bit by bit:
A) Adding more stops would spread out the passengers, and C:S calculates the number of buses used by a line based on its length. This bleeds into B, C, and D. Do you want many short lines with a fewer buses? Or fewer long lines with lots of buses? I'd err on the side of a larger number of smaller lines. It will divide your passengers up between the lines based on where exactly it is they're trying to go. Intersecting these lines will allow them to hop from line to line more efficiently.
E) As far as I know, adding additional bus depots does not increase the number of buses spawned. The only reason you might want to do this is to decrease the initial transit time of the buses when you create a new line.
F) Yes, adding more to your bus budget will increase the number of buses allocated to your lines. This is the easiest, most surefire option, but also the most heavy handed and expensive.
Here's a SimNation article that goes into more depth on some of these topics.