So, everything is now cut and even mostly pinned together (though I ran out of pins and miscalculated the number of squares I would need in one fabric, which I haven't had opportunity to cut yet).
Since I'm using the purple for the sashing I won't use it in the front blocks. I decided this after having cut all my fabric, though, so I'm going to go ahead and make the blocks with purple in them and then use them in the backing somehow.
The overwhelming advice I got about the backing was to NOT use the knit, and as a beginning quilter I'm going to go with that. (Plus tax refund, woo-hoo! So I don't mind so much buying more fabric.) I'll use the knit for something else, maybe a softie. I plan to go back to the store where I bought all my fat quarters and see if they still have some on the bolt, using one of those or something compatible as the backing, with the purple squares as an accent.
No questions this week, just excited to get sewing! It's been very interesting to see how things look when chopped up small and I'm curious to see what it's like once the seam allowance is also taken up.