The thing is, if he's going to dump you because of stereotype or whatever, that's going to happen anyway, and it's on him. You can only be you. In many ways better to get that over and done with ASAP.

I'm in my 50's and have learned that it's something to bring up early on. The sooner the better. Worse in some ways for me because I've been in poly relationships in the past, and that's also a dealbreaker for some people. Which, you know, I'm not here to argue with them about that.

Focus on the stuff you're talking about above: this is what you want from your relationship. It's all about you two, not about your sexual history or preferences or how you might feel in another place and time with someone else. "would you still love me if I was a blue whale" sort of questions are silly.