In this option there should be a way to give a formatting for the frame names (For example ffmpeg uses fixed digits) and give an information message or even handling when the path is a folder (for now it just doesnt export without any warning or error)

In case of JPG format i believe there should be an option to choose which color to use as a background (some probably prefer a different color than black)

Thank you for the feedback! Concerning the background: You can set the background color under "View > Set background..." in the main menu to any color and also include a background image.  But what I think needs to be done is to inform the user that jpegs don't support transparency or as you said offer a convenient way to set the background color from the export dialog. 

I thought that background color was just used it the editor/preview .. well i just messed around with it a bit so didn't check everything!

Happy to be helpful! :D Keep up the good work! This can become a great tool