Open relationships are a strange thing, especially when they're fairly loving. Er, so to speak.
I'm not in one now, but when I was before, I would regularly send my girlfriend to sleep with her ex. I'd slept with him, I knew him to be a loving individual, and their relationship ended very casually and well. My own breakup with that woman was not because she was cheating, but because she lied about a great many things.
I find it interesting that I do not seem to be a jealous person. I remained a good friend of the "other man" for quite a while after the Big Reveal, and our distance now is literally that of proximity. Every time we see each other, there's a hug and a catching up to do.
How many is too many? I can't say. In general, I seem to prefer women in their mid to late twenties with a fairly healthy history of sexual experience, preferably more than myself. So it is with great irony that I fell in love with and married a woman whose virginity I had the privilege to take.
Our relationship isn't open, and I'm fine with that. I am, myself, rather monogamous thus far in my life. (I'm nearing 30, so there's still time for me to be wrong, but I do have some context.) I am her first sexual contact, whereas she is probably my fifth or sixth. I'd have to work that one out, I always forget. There was a very busy month there. And that's not counting second base with another partner long ago.
I sure hope that's not too many. We seem happy.