My first poly experience after a 10 year marriage was with a guy who'd been a friend of mine for 3 years. There were certainly jitters and anxious and nervous feelings on everyone's part, but my husband and I had talked about it at length, and it was a few months between starting to talk about it with my friend and anything happening.
It ended up being a very short sexual relationship with him, but we are still great friends 7 years later, and I felt safe to try with him because I knew him long enough to have a good sense of the type of person he was.
The one warning I would have, and the one negative of my experience was that I loved him as a friend, but his feelings for me were a lot more serious, and that is the one reason I wish I hadn't gone there. We managed to get through that, but now that I am dating again after a 6 year hiatus, our friendship is having growing pains from what I believe is jealousy about it - even though he's happily engaged. Might be one issue for you that could occur later if it doesn't work out or you end up having unbalanced feelings, but that's one of those risks you always have to take when dating friends regardless of mono or poly.
The great thing about where you are is - there's no need to rush. You don't need to go on a date with this guy next week or next month, and if you take it slow you can practice flirting, and have time to figure out how everybody feels about it, since once it happens you can't take it back!