3M medium grit sanding blocks should be all that is needed.

3M Between Coats

Also-

Remember...that stuff cures-out with UV-exposure. It's good that you'll have gloss under the Satin! Higher-end floor refinishers sometimes do it that way, because the glosses are a little "tighter & harder", than satins.

Faron

Many thanks for your responses. We went out yesterday AM to look at our "horrible" door, and we were astounded. It was like professional refinishers had come in while we slept and redid the door -- it was gorgeous! Yesterday evening we started lightly sanding, but it was still a little soft in places so we will resume the light sanding tomorrow (raining today) and apply the final coat as soon as rain and humidity allow.

Final questions: since it looked so beautiful yesterday AM, we now plan to apply a second coat of gloss instead of satin. Any objection? And, finally, after the second coat of gloss, do we do a final sanding? It looks so beautiful now with that glossy finish that we don't really want to reduce it. Thank you.

No, don't sand the door after it is done.

To paint the glass door, you have to starting paint with a top panel of the garage door. To paint garage door you must start with the corner of the door. I will suggest you that latex paint is used to avoid the imperfection, you have to sand the surface of each panel with phosphate trisodium to remove grease and residue. A premier coat is necessary only if the enamel is taken off.

Here is a link that might be useful: painting company

This post was edited by LuisHinkle on Thu, Aug 28, 14 at 9:12

Final Outcome: The door looks beautiful! Thank you all for advice and encouragement. The Sikkens was a great choice and was very, very easy to apply. Thank you all again.