I would pre-wash the fabrics and then starch with whatever you prefer (Starch/Best Press/whatever).
To mark, I would use a very light, thin line chalk pencil if the fabrics are dark, or a very light touch with a water removeable blue pen if the fabrics are light. The blue pen comes out with just a touch of water. I usually keep a damp cloth handy to dab away the lines as soon as I don't need it anymore. I soft brush will brush away the chalk lines. Jamie Wallen uses a chalk pencil to mark called a Boehing or something like that. I think he also has a video on marking utensils.
Being careful not to quilt lines close to each other in a back and forth motion will help keep the loft smooth between lines.
Don't wash, obviously.
Can't help with washing the batting. If the item is never going to be washed, I don't see that it matters.
I hope we get to see your creation.
Watson