Thanks for the info. I am uploading a mock-up now.

Also I agree with @eishiya - would love to see a mockup! :)

pico-8 is such a lovely palette

That's not an issue. Mock-ups are accepted all the time. In a mock-up, you're still choosing where each pixel goes by hand, you're just repeating some pixel patterns (your tiles) using a shortcut (copy+pasting). Rule 6 is intended to discourage the use of techniques which take pixel-level control away from the artist. Repeating tiles is as harmless as using the fill/bucket tool - even if you're not manually placing each pixel by hand (that would be nuts in larger pieces!), you're still in full control of everything.

I agree, but being new to the site I was concerned that would be a violation of rule #6, since each pixel would not be placed 'by hand' if I did a mockup. If that's allowed, then that is just my ignorance - 

1. Any art you post should be PIXEL ART! Pixel art implies that each pixel is placed by hand (no filters, paintbrushes, gradient fills, etc).

I recommend making and uploading a mockup instead of the tileset. It'll make for a more appealing image, and allow people to give you better feedback. It's hard to gauge a game art without seeing it in use.