I would certainly insist on dealing with the std testing first. That is a health issue. Our health is vital to our life.
I would also take the advice of sitting down and creating a "what is it I think I am looking for in poly" list.
Another good lead in for that is in the book Opening Up. We used it-it had WAY more information then we'd ever need, but it covered all sorts of possibilities and some of the ones we didn't think of-were pertinent.
More than anything else though-be good to yourself and work on you. Because no matter if you stay in poly, go back to monogomy, stay married, get divorced etc-you will always be stuck with you, so make you the best you that you can be!