Use a shorter stitch, when I sew to a foundation I try to use a the smaller seam because of shadowing. If you use the smaller stitch and then top stitch, that should eliminate most problems. I did a quilt once where I serged the some of the different fabric edges prior to sewing because of raveling. It didn't add any unslightly bulk to the quilt and kept the fabric intact, AND I can wash the quilt.
My rule of thumb when using plaids is I use a geometric, a floral (print) and a solid, this helps break up the plaid.