Alen and Jymsar will be the only true romance-able characters, though you might get to have fun with other characters in the main story.
As far as the Simulacrum goes, lots of things can happen in there. Depending on how things go and player feedback, we might see old and new characters be featured in the future, though some characters aren't likely to be featured (so far: Harren, Gemmaborg, Chilas, Jymsar).