Hey, I'm glad you liked the game! :) I'll do my best to answer your questions, but some things tie into later plotlines so I won't give out spoilers for future content stuff.
1. Side girls won't have heart cards, no. Those are only for the Main Girls. Part of the fun of a sandbox game is discovery and sharing finds with other players, so the game won't hold your hand in every area.
2. I have no plans to add dragon girls, largely because there's already too many characters in the game :P However, it has been requested before so I may add a dragon girl scene to the Nexus, possibly.
3. Most girls won't seek your attention simply because that would become incredibly chaotic and quite frustrating for players very quickly. Some people are already annoyed by Gwen's texts and things, so having another ten or so characters doing that would be a nightmare for them. You'd have to potentially click through eight separate scenes every time the in-game time changed ;)
4. There will be no difference in the character's storyline if you used awaken or just romanced them. Aide characters that you have a choice of awakening or shattering will make a difference though.
5. I'm a huge fan of Lovecraft's work, so there's deliberate cosmic horror references in the game and there will certainly be more to come. Though I'm not trying to make CK into a horror game so there shouldn't be anything too stomach-churning in there ;)
6. Yes, there will be more money sinks - eg. Items you can buy at the bar to unlock dates/events with the girls. Most of the money sink options will be added during the final passthrough of the game, but a number of them will be put in as I go.
7. The interfering is going to happen in Act Three :) I don't want to put it in Act Two because it could badly mess with people trying to do the girls' storylines or follow the main story.
Hope that answered all your questions! If you have any more, or want clarification on anything I said, just let me know :)