Cross-hatching would look fine. You could stitch around each of the blocks and possibly around the center object and the cross hatch in the white area but not thru the blocks. The blocks would stand out better. I think your son will love your labor of love. Years ago I made my son (when I was pregnant) a block quilt and today there are only threads (litterly) left of it but he won't get rid of it; he's 26. I'd love to find the fabric and make him a new one. I knew nothing about quilting back then; I tied it like I had watched my grandmother do. It'll be well loved no matter what you do. Check out Leah Days web site on FMQ; she's great and she does it all by a regular machine and if you ask her a question she'll try to answer you.