My only real advice for OP is:
-feel really confident that you can be honest and communicative with your partner before diving into this.
-just state what to want to potential partners up front. Get used to rejection, as this style of relationship isn't palatable to everyone.
-it helps to acknowledge the pressure being put on any unicorn you court, but still stick firm to what you want
-it really helps that you can spell. Most of the unicorn hunting messages I get on okcupid are unintelligible, so you're already ahead of the game.
-You might want to get your training wheels at a swingers party. Ever thought about that? Those things are usually full of willing unicorns, some open to the idea of poly
-A triad I knew just up and started bringing their third to family functions and acted like it was normal. They didn't come out though. Shrug. If her family is super liberal, I would honestly just give them a chance. Poly is coming into the media a lot more now, becoming normalized, and it gets a lot of positive coverage.
-for god's sake, don't use craigslist