You can set the special media type 'Animated GIF'. This will preselect the GIF format for when saving an animation.
A GIF animation can have a transparent color. Just enable transparency in the layer settings if required.
Pro Motion is not a GIF optimizer, but the files that are created should be small enough. You can change some optimization options in menu File->Project settings... section GIF. Generally GIF files become smaller if you use an equal palette for all frames and if as least as possible colors are used.
The menu Colors contains certain functions to reduce animation and image colors.
For saving animated GIF files use the corresponding file type from the save animation dialog.
Last modified: 17 March 2017