We can deliver any format you wish to use, there are no requirements on our end about that. :)
As for size, the largest single file that can be uploaded to our servers is 500 MB, which may not always be enough depending on the length of the video. But by the time you have enough space in your account for a 500 MB file you're already going to be on the $18/mo plan, which also supports remote hosting.
Remote hosting allows you to store much larger files on your own server or with a service like Amazon S3, and remotely stored files can be as large as 2 GB each which should cover a reasonably compressed feature length video. Remotely stored files also don't count against your local storage limits so you can sell as many as 60 different large videos on the $18 plan as opposed to just one smaller video.
Our help page here explains how remote hosting works: