That's right, after the demo, you/MC will be able to start making choices based on who you want to romance and how you want to interact with them. To your question, I've checked the script, and the number of choices in the full game ranges from 10 (Thrace) up to 15 (Iandir). The choices will be more specific, like what you have seen in the previews : ) There will be 1 good ending and a few bad endings per love interest too, depending on the choices you make.
Estimated gameplay time of the full game should be around 20-30 hours, depending on how one plays and how fast they read.
Thank you so much for asking this, by the way - I will put up all this information on the project page for anyone else who's interested!