Hi and welcome to the forum!
Reading your short intro, seems like you are in a good and happy place to start your poly journey. In one happy relationship and open for more... Are you and your girlfriend planning to date separately?
This forum is packed with good information, advice and stories of the real life. I would suggest you (and your gf) read a lot, and you'll be better prepared for the practical poly life when the time comes.
I am a woman with two male partners: CJ (legal husband) and Mark (no label added).