Re: novel writing
i believe writing is like anything else, you've got to practice at it. assuming you're not some wunderkind at writing, remember that it's important to write bad stories, too. hey, some would say that's all *i* write, heh heh. not saying yours is bad, haven't a clue, just saying that even if it is, finish it anyway. you have to get the bad stuff out of your system.
is your scenario common? not knowing a lot of wealthy people, i couldn't say. it's probably like anything else, humans invite drama into their lives by virtue of ignorance, stupidity, lust, greed and selfishness. rich people aren't special in this case: indeed, part of the premise behind why my WIP characters have so much drama is because they're rich and bored and have nothing better to do than play mind games on each other. and where there's drama, there's sex, so, yeah, totally plausible to me.
i think it's okay to second-guess yourself... to a point. correct me if i'm wrong, but are any of us such a genius that we defy every convention and yet still make a brilliant story? from oaters to bodice-rippers to a rag-tag band of fantasy character out to save the world from the darkest evil the world has ever seen, again, whatever we do has probably already been done in some form or another, so don't worry about being 100% original unless you enjoy migraines. so, as long as the market isn't saturated, as long as you do a good story, it should stand on its own merits and be entertaining enough for *someone* to give it a read, eh?
you're always going to find someone who says 'it's been done,' or 'wasn't that in the news a few years back?' stay away from cliches and predictability and even the old work-horses of storytelling can be made into something good to read.