I'd do the 1/4" seam after pre-washing and shrinking the flannel well, it sometimes shrinks very strangely. And I would use a walking foot to quilt it if you are doing straight lines. You could probably do it without, but it makes sure everything feeds at the same rate and since you are sewing in the middle of a large piece you don't really have any reference to see if something is off until you get to a cross seam or the end, where if you are sewing a seam on the edge of the fabric you can see a little better what's going on.
I rarely change the tension on my machine - the only way to tell is if your stitches dont look right. And if it were really thick you might need to lengthen the stitch, but I dont think for this you will need to.
My biggest question though is without any batting are the lumps from your seams going to show through and be rough?
Last edited by shnnn; 02-21-2012 at 11:33 AM.