Sooo ... threesomes only at first, transitioning to "dyad sex" later on after all three of you are more comfortable with the relationship? (See, I'm having a hard time getting that right too.)
Everything made sense I think, it is good that you are trying to shoot for a poly environment in which everyone doesn't feel constrained by rules, rules, and more rules. Open, flowing, and natural is good. See if you can't make that happen.
Much luck and love wished to you!
Love means never having to say, "Put down that meat cleaver!"