The script player_load_starting_coordinates is called to load all the starting coordinates normally, if you changed the start flow (e.g. skipping the player creation menu) you might have removed that call so it won't happen. (Try adding a debug message to show global.saved_room_pos_x / global.saved_room_pos_y when loading - if they're different from the coordinates you defined something is wrong with reading them)
If you remove all classes, you should set the macro to 0. (It's better to have a placeholder class that has the default stats, though - they're used when finalizing the character customization)
The connector biome has a very neutral tileset and no music, it's inspired by the loading rooms from Symphony of the Night:
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Only background doors can take arguments. These arguments are the map cell for the target room (you can see this in the world map editor). If the door doesn't do anything after opening, that means there's nothing in that cell on the world map. So basically these doors are teleporters.
One-way doors work the same way as normal background doors, but you need to open them from the back before they become usable from the front side.