I honestly believe Felix was gay, not bisexual. He seemed more interested in affairs with men than with women. Irina served as his beard, although I don't think Felix cared that much about his reputation She was from a good family as well as a vessel to produce an heir, As for Irina, there is so much about her we don't know. I agree with whoever said she seemed to have no personality. Of course we don't know if this is true or not, but there really is not much information about her. We never hear about her experiences, her opinions, nothing. True she was shy, but lots of other people are shy, yet we still get an impression from them about their character. We hear she was considered pretty, this is subjective, all of us can look at her pictures and have our own opinion on her looks. As for her being fashionable, well, this is what young women of the time were wearing if they could afford it, I do not see her as some sort of trendsetter. She was a married woman and of course there is going to be a difference between what she and OTMA were wearing. Perhaps she really was asexual as someone else said and didn't care for that side of marriage. If so, she was the perfect wife for Felix. As for them having more children, considering that they grew up with nannies, they probably couldn't cope with the one they did have. They could not afford to hire help, and they couldn't handle the day to day adventures of child rearing and the reality of raising children without wealth.
As for who could play Felix in a movie: There is an actor that reminds me of his, not so much in looks, although he could be made up to look like Felix. but the flambouyancy that Felix is said to have had. He was on the soaps and played a transgender character. Check him out:
http://www.youtube.com/watch?v=Nx0rinDFGd8