When I get some I am either going to go with table cloth cover from JoAnn's or a clear plastic shower curtain from the dollar store......guess which I'll try first, lol!
I have stitched on several pieces of vinyl and used a bit larger needle but be careful because having a design with a lot of stitches will perforate the piece and it will fall apart. The foam backed vinyl (lunch bags)is especially bad for that.
I guess it would depend on what you are using it for. I would probably go with the medium weight. I used a top stitch needle, but that would depend too on what you are doing. Some people will use tissue paper over the vinyl when they stitch, then tear off the tissue paper - I did not, and it turned out okay. Good luck with the project. Oh, - I did the bugs in a jar shirts and they turned out really cute.
Is the tissue paper to make the foot move smoother over the vinyl? H&* for all.