How many folks here had a preconceived idea of a relationship model that you wanted before trying?
I most certainly was ONLY ever interested in monogamy and in fact had quite a set against non-monogamy. Swinging, group sex and Poly just seemed kind of sleazy to me, before. Non-monogamy/open relationships somewhat less so, but still didn't appeal to me. I can honestly say I'd rarely ever even considered such things, insofar as they might relate to ME and my life.
How many people are in that style of relationship?
After a mono marriage lasting over 20 years I am no longer in that relationship. I fell in love with someone else, effectively ending my marriage two years ago (though there were other reasons)... but "stumbled" into poly when a complicated set of factors meant I ended up falling for a second person who happened to be my male lover's former lover (female).
Is there any people who are still with the original people they transitioned with?
I am still with the two lovers mentioned above, yes, and have been for two+ and one+ years respectively.
I never learned to date. Most of my lovers have been friends who showed interest in me, so there's a little dearth of the societal "pursuit" model.
I get the impression that, for most people, "dating" means "mate-seeking" -- for me, maybe "having a fun social time with a person I find particularly interesting."
Like you, Ravenscroft, I have never really "dated", not even when young. Almost without exception my lovers have been friends/friends of friends or work colleagues first, so I already knew them in a social sense before falling for them in a romantic sense.
I have never gone on a blind date, joined a dating website or used a matchmaking app, or actively "looked" for a mate/partner/lover.