Andy,
Thanks a lot for your input. I exported it as H264 and it went a lot faster this time. (I set it to about 500 kbits/sec for the test run.)
My next question is how to preserve the aspect ratio.
The canvas is set to High Definition 16:9. This is what it looks like in Motion:

When I exported it, it bunched up like this:

Do you know how I can fix this?
Thanks again for your help! I am so very very grateful.