I'll answer what I can:
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Are there comfortable harnesses out there?
I ponied up for the Skipper's harness in the Hobie catalog and have been very happy with it.
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Without dropping my sails, is there a proper way to set my sails so my hobie doesn't sail off if I abandon it for a few minutes?
I've never left my boat without either it secured or with someone who knows how to sail it. I don't think it's a good idea to leave your boat since the wind still has an effect on it, even if the wind only pushes it downwind. And unlike monohulls, a cat doesn't pivot easily and instead will move until pointed into the wind, which means you'll be swimming to get back to the boat, and you better hope you can swim faster than the boat can drift.
Stay funky.