Welcome to the wonderful world of quilting. Seems you are already hooked, but if you aren't, you soon will be. LOL. Using 6 wide strips for the top will be good, or you can cut more, narrower strips to give your top some variety. Any quilting cotton fabric will do for the backing -- you can choose a color that is in all 6 of your fabrics to do a solid back, or you can take your favorite fabric from the 6. That goes for the border(s), too. An inner border is basically a stop for all the prints and outlines them, and an outer border pulls all the prints together. Be sure you watch some good tutorials on how to measure when you get to the borders, because there is a right way and a wrong way. My opinion is that you don't use a very light fabric on your outer border and your binding, because that's where it is handled the most, so will get grungy. But, like I said, that's my opinion. You can do batting and backing, or you can do flannel, one layer or two, if you want a very light quilt. If you use flannel, be sure to wash it before using it, because flannel shrinks a lot. There are several on this board who I've read that posted that they wash and dry their flannel fabric twice, just to be sure. Fleece is OK, but you are right, it does stretch, and it stretches more one way than the other.
There are a lot of good tutorials on YouTube and on blogs, so between the help you will get from board members and the internet, you have a lot of information at your fingertips. I would suggest that if you have a LQS (local quilt shop) in your area, see if they offer a beginning quilting class and take it. There's nothing like being able to ask questions and get answers right away.