This is cute. It is completely your call, of course. I would tend to do stitch in the ditch along block lines, then remove pins from the blocks and go back and play with FMQ. For example, a heart or star on each 4 patch, maybe flowers or vines on the border and outline quilting about 1/2" out around each buggy. I'd use yellow for the SITD and red or multicolor for the FMQ. the SITD controls the position, so you don't have to be concerned about any pins as you FMQ. I am also fond of writing with my FMQ. I might write the words to You are my Sunshine around the border or this very sunny quilt