Yes, you would use spray starch for the quilt top.

For the backing, however, what I do is mix a 1:1 solution of Sta-Flo liquid laundry starch and water, "paint" this onto the backing fabric with a cheap, large painter's brush, allow a couple of minutes for the fabric to absorb as much starch as possible, toss the yardage in the dryer, then iron with steam. As long as you iron somewhat with the grain (in other words, don't try to push the iron along the bias!), you will end up with a very flat, very stable backing.

For the quilt top, you will not add any more distortion by "pressing" with spray starch. When I looked at your previous photo of the top, I think some of the distortions were from cutting and sewing issues; not all of it was due to your ironing methods. You may be surprised by how much of the distortion becomes unnoticeable after quilting and first wash.

With such a small quilt, and using W&N, you really do not need to add horizontal stitching. However, lines 10" apart are not enough for a crib quilt which will get washed frequently. 4" or 5" apart would be as far as I would go. Closer than that would be fine too; however, a lot of really close lines using regular 50wt/3-ply thread can add a surprising amount of stiffness. If quilting lots of close lines, I would use a polyester thread or finer weight cotton thread.

Are you planning on using a walking foot? I highly recommend that.

If you Google "wavy machine quilting walking foot" and then click on "images", you will find lots of examples of wavy line quilting for inspiration.

If you have poufy blocks I would steam the heck out of them to shrink into shape. Sometimes I wet them too. Do this before you use your spray starch. Ironing is dragging your iron back and forth on the fabric. Pressing is putting your iron straight down only, no back and forth or side to side. pick the iron straight up, check to see if it is dry. If not, repeat. When dry, more to next place and do it all again. Some people spray the whole top and let it dry on the ironing board. Then use steam to PRESS it.

I don't, but I usually do my vertical lines fairly close together, usually 1/2" to no more than 2" apart. I also mostly use Warm and Natural or Quilters Dream batting.

I mostly do FMQ, large stipple, large meander. I quilt no more than 3-4 inches apart. I would be horrified if the batting broke apart and bunched up. I donate most of my quilts.

I like your wavy line idea and starting from the middle and working your way out is good too. I would actually start near the middle for each line and stitch out to the end, then after all the lines are done going one way, turn it around and pick up those lines and go the other way. You'll have some lose threads to deal with, but this method will assure that you don't end up askew when you're done.

May I suggest that if you need to take up some puffy areas and you are a beginner DMS quilter, like myself, you might consider "embellishing" those wavy lines my turning them into a wood grain, or elongated leaf pattern. It's really easy to do, it will help you take up that extra pufffiness and it looks super professional. I'll see if I can post a picture for you.

~ Cindy

Yes, this is how I do my quilting, too. I feel it keeps everything "balanced."

This is what I do with all my quilting. It works very well. Some day I will take the time to practice "fancier" quilting but for now & craft shows this is the best.