I like your colors and the way you placed them. On a rail fence I usually let a predominant color zig zag diagonally across the quilt. Just goes to show, new ideas are always popping up. Especially by beginners.
As to quilting: Since black is the strongest color, I'd use black thread for quilting the body and blue for SITD. I'd use a walking foot for the body and SITD foot for SITD (it has a guide that opens up the bend in the fabric and helps stay ITD). For the body I'd stitch down the middle of each rale and let it continue across the perpindicular block to the next rale, both across and up/down the quilt.