I would definitely suggest waiting and dating, even for as long as a year. Triad dynamics can be very tricky and prone to changing and evolving. Best not to put anyone's living situation on the line while you all are feeling that out.
This is an excellent set of advice, for your gentleman friend and for you and your partner: http://www.morethantwo.com/coupledating.html
I think the most important question to ask right now, while you're still in the giddy phase, is would it be ok if he ended up developing a relationship with one of you but ended up just being friends with the other? I and others wrote at great length on this question and related thoughts here: http://www.polyamory.com/forum/showthread.php?t=23779
Best of luck!!
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.