My first quilt class (1976-7) had us make a block each week, increasing in difficulty and using a variety of skills. My original group of fabrics was too large and I ended up setting aside all the blocks with a couple of fabrics that didn't look right with the rest. Finished quilt has 20 blocks, 8 fabrics in the blocks, including a light and a dark solid, with sashing between blocks.
I would recommend 8 or fewer fabrics, making sure any combination of them looks good together. I like your idea of having the sashing match the background of the blocks, but not all pieced blocks have a "background".
(Six blocks that got pulled out ended up in a quilted jacket.)