Ponch, since you've pulled it off well, this might be a good opportunity for you to share best practices with us on how you set up your games. Each background is a different room, with a GUI for options? Buttons take you to different rooms? Invisible player?
1) Invisible player (a small 4x4 square).
2) Each background has it's own room, unless the background includes a simple animation (for example: DuChamp leaning back from her desk)
3) Two kinds of rooms: Rooms with no choices, only text; Rooms that have choices that branch the story with the two button GUI.
4) Lots and lots and LOTS of scripting.
Seriously, every time the player clicks the "next" arrow, there's scripting. Each dialog button? Scripting! Player leaves the room, check the script to see what choices they've made so far that decides what will happen next. Player enters the room? Check to see if they're carrying an inventory item so we know what will happen while they're in the room.
To be honest, it's not really all that different from making the usual adventure game (in some ways it's a little easier). But in a few ways, it's more work than I expected. If I had to do it over again, I'd make a better outline (probably in flow chart fashion) so I'm not constantly checking my notes to make sure I'm not missing a narrative off-ramp and messing everything up.
Also, I wouldn't attempt something so new on a MAGS schedule.
Who knows, maybe one of these days, I'll make an OSD visual novel and release it as a template.