I use the edge of the walking foot for my spacing guide, roughly 1/2" apart. On my Bernina 1090, stitch length 3 is best for straight line and stitch-in-the-ditch quilting. Notice I've left a gap in the center of each strip. The gap is roughly the same width as the sashing strips. I work toward the center of each strip, three rows of stitching from each side. The gaps hide any unevenness. I also stitch all in one direction for the entire quilt so there isn't any bias pulling that might result from going down one side and up the other.
This quilt will someday end up being a donation for a children's charity. I like children's and baby quilts to be more soft than densely quilted. The more densely quilted a quilt is, the more rigid it feels. Narrow channel quilting is good because it gives the look of closely spaced quilting, but since it runs only in the vertical direction, it results in a less rigid quilt than one quilted every 1/2 inch in both directions. It's sturdy enough to hold the quilt sandwich together through whatever abuse and washing a child's quilt will get. I've used channel quilting spaced 1-1/2" apart on other quilts and it holds up fine.
Next up, getting the binding on and stitched down. Hopefully I can get it done today and show the finished quilt tomorrow.