Beautiful quilt top!
I would look for a walking foot. There are several companies that make walking feet that fit various machines and they are in the $30 range. I have gotten them for older Viking and Singer machines. I bought them at a shop that sells sewing machines but I'm sure they are available on line as well. I even got one that fit an old Singer with the slant needle. I have them for my Featherweights too.
I wouldn't start out with free motion quilting without a lot of practice first. Stitch in the ditch can be challenging as well as your stitching has to be very straight an accurate. Maybe some stitching done a presser foot away from a seam line would work. No marking other than perhaps at the corners.
At the beginning and end of a stitching I leave longish threads, tie them off and then using a big eye needle run them under the surface, bring the needle off and cut the threads off there.
Consider how you want to sandwich the top, bat and backing together. Some use pins, others hand baste, others spray baste and others (me included) use washable glue squiggled on in a fine line on the batting then attach the front and/or back. There are lots of discussion on this board about this step.
Good luck, you are off to a great start!