You are doing great and your questions are good questions.
I'm sure that you will have answers to you questions. While you are waiting on the answers you might go to the top of this page and click on the word "search" and then enter in "quilt sandwich". There are lots of threads there and some may answer your questions better than I can. Make a small sample of quilt top fabric and 1 layer of fleece and then try 2 layers of the fleece and see how it feels and sews. Fleece may stretch a lot so take that into consideration. hope this helps. I learn by doing. Happy Quilting.