If the fabric is just thin, I wouldn't call it fragile. Fragile is a quilt that is fraying and has worn spots or holes. On this one, I would just do a stitch in the ditch 1/4" away and something pretty in the yellow squares. I agree hand quilting would be nice, but many vintage quilts I have from my grandmother (60-100 years old) are machine quilted. I do think a vintage style of quilting would be nice which is why I though a straight line quilting appropriate. As for tying, I think that is more for utility quilts than such a lovely pieced top. Regular quilting, fairly close together, will distribute the stress more evenly.
Pam