Re: avi file size

Did you render it uncompressed?
Hard drives are very cheap these days so there's no reason not to have a 2 TB. one on your system.
This is in addition to your system drive as you should always have at least two drives on your computer.

You can drag a a still out to make it as long or as short as you want.
If you're referring to the default time, that's found under Options - preferences - editing - still image length.