I agree with Kyle, take it slowly. I speak from experience because we didn't take it slowly, at all, with our quad. It backfired and we took a step back for quite some time (in part because I had a baby as did the other girl of my quad) and though we remained best friends the whole time, being slow would have made a huge difference. If you base your relationship on friendship more than sex, it will be more fulfilling and last longer.
39 years old, married (almost) 17 years to Avatar, in quad relationship for 2 years with Busbuddha and his wife, 3 kids between us. Have been practicing non-monogamy for 8-ish years.