Quite a lot actually. The main storyline, major twists, antagonists and ending were planned before the first release.
Most characters were prepared beforehand, though, as I got better with CharaStudio and Charamaker I made a lot of improvements. Only recently I tweaked skin textures of all current and future girls, their skin will also react better to light sources which will be clearly evident in one of the scenes in 0.4 release.
As for h-content and mind control - I know more or less what type of scenes I want for specific girl and how will protagonist's power affect her. I played a lot of japanese saimin/mind control games in the past so I have a rather large pool of ideas when it comes to this stuff