I completed a usable staircase today, so now the player can move between the floors freely. Will most likely pretty-up the staircase during the Production phase. I've also fitted door frames into position, but when I did I realised I'd made the upstairs rooms too tall compared to downstairs, so the door frames were too big for downstairs. That will be fairly simple to fix though, I'll just need to adjust the heights of the door frames and the upstairs to match those of downstairs.
Also started thinking about lighting for inside the house. May just [unrealistically] place point lights in strategic areas, or will use multiple dimmed directional lights. At the moment it's quite dim, I've just placed one point light in most of the rooms.
Haven't managed to pull together the script for the Level-access mechanic, but I have collected various scripts that could be handy to mash up and put together and written out a basic outline of what the scripts need to do.