I think that if you have a strong contrast, you can get away with almost anything. I'd lay them out before sewing together, to make sure like is far away from like, and tone apart from the same tone. We look at a quilt on the bed or hung on a wall as one piece with different "pieces" springing out at us. These should be sprinkled all over the quilt, not one big blob of color here and another color running into another.
A monotone is restful, but you said that nothing was going to be duplicated, or as I understood it.
PLease let us see the finished quilt, it sounds delightful.