I'm interested in this, but I haven't made a level or tileset in a long time. All of my levels feature at least one (usually more) of my own tilesets, and of course my own level design. I also may be mistaken but I think all of my levels feature only my own gradients, but again, there may be a default one in there somewhere.
Regardless, I'm interested, but I would need to know exactly how much commitment would be required. I also don't know how well my art would blend with what is wanted, since I can only do a few styles well, and everything else just looks messy.
So basically, I can do anything on the list, to a degree. Just know that I'd have to know a bit more before actually committing to anything.
EDIT: As an additional note, I consider myself better at tilesets/leveldesign/gradients than my released levels dictate, but they are still the only complete examples I have.