Mixing was simple, I just followed the directions. No quirks I can think of. I will say that it was fun watching the various solutions change colors as they were mixed.

As for how long they'll keep, I don't know. I put them in PETE bottles compressed down to eliminate airspace. Next time I use 'em and have the bottles emptied temporarily, I'll pop 'em back into shape and fill the extra volume with the marbles my wife brought home for me. But I've got enough film to process that I'm worried more about exhausting them than keeping them. And I don't have any previous experience with the kit to rely upon.