Mkotch gave some good stuff, I'd say you don't really need a walking foot, it will help and is nice to have, but I went without for about 30-40 years myself.
As said, follow the instructions given with your wadding/batting. It will be unlikely with most batting to have less quilting than about every 4-6 inches apart, but it varies greatly. There are structural reasons for quilting, I can tell you from my own early quilts, it is not the seams that fall apart but the big areas of unquilted fabric rots out. I personally prefer puffier batts with less quilting than is currently popular, but that is still more quilting than I did at first. Do not wash first, but if it has been in a bag lightly air fluff it a bit (couple minutes) first on air/with minimal heat to get the creases out, or spread out and let it rest for a day or two.
Always test your stitches first on a separate layered piece of fabric/batting/back to get your stitch length/tension correct. You will need a reasonably large needle for the quilting part, probably at least a 14. You might want to use a top stitch needle, I typically just use universal needles.
I prefer to spray baste. A lot of people here recommend glue basting, I keep saying I'm going to try it and people keep giving me old cans of spray baste to use up. I have a small house and it is not ideal but my queen sized bed is my largest available space. I take off the blankets and pillows and cover my bed with kraft (heavy brown) paper to use it as a work surface.