Sorry about the first 2 suggestions, the game is now officially cancelled. The play game door is just there if I ever got around to it. It doesn’t exist.
HOWEVER I do have some good news for you, for your bigger start idea. There is a work around, you can place the start on the center of where you want it to go, then fill the empty space with checkpoints!
Also, it’s already possible to add different keys to different doors! The key you place will only open the door on the same layer. So a key on layer 1 won’t open a door and layer 2. Same goes for gold doors! The gold doors will open only if the coins on that layer are collected. The buttons to switch layers are on the bottom, and to use gold doors, it’s the plus and minus sign on the keyboard while you have selected the doors
Hope this was useful