I knew about polyamory from friends, but my spouse encouraged us to try it in order to get his needs met.
What didn't work well: his desire to move quickly, and thus I missed out on time to really sort out what would work for me and what would not. This was frustrating for both of us, and was impeded by poor communication skills. Also, trust was somewhat lacking, because my spouse had had affairs in the past. We didn't agree on the boundaries very often and I rarely felt safe, especially in the beginning. I felt that I needed a lot of boundaries in order to know what to expect might happen. I also tried to place boundaries instead of asking for respect around specific needs. He would have prefered not to have any boundaries at all. I was often emotionally exhausted trying to cope with the amount of change constantly happening, and it made me much less articulate than I am capable of. I needed a lot of support, and didn't reach out as extensively as I might have. I was also not firm about getting my needs met, because I was afraid it might end our marriage.
What did work well: he was very supportive of my first experience with someone else. I think occasionally, he experienced some surprise at his feelings, but didn't display a lot of jealousy and seemed genuinely happy for me. Compounding this, although my lover was also inexperienced, my metamour was not, and she has been our friend for quite some time. There was a lot of trust already there. She supported us all in that particular transition. My lover and my metamour also had clear expectations and desires, making it easy to decide if I wanted to be part of their lives in that way or not.
What else worked well: helping choose my spouse's lovers, and having open communication with them. Not that I set him up on dates, but that when he expressed an interest in someone, I felt better about it if I were encouraging and aware of what was going on from the beginning. I once brought in one of his lovers from out of town for a surprise visit, and I really enjoyed meeting up with them later in the day and seeing how happy he was.
Good luck, and good for you for gathering information first.