I think the bedroom and bathroom were moved to the second floor because too many people were constantly using the toilet to avoid sleeping every time, this breaks the gameplay a bit because you can just use the toilet and don't sleep to get a lot of free time instead of constantly working. About extra plumbing: there are many small houses that have toilet and bathroom on the second floor for convenience, and there is a reason to put a bathroom near the bedroom. Also, the developer wanted to make player explore the base more, and putting the bedroom on the second floor forces the player to go around the base instead of sitting in one place.
There is an empty space on the second floor between two rooms where can be another room, and I think the radar fits perfectly into it. This way players will be forced to walk around the base to see if there are any entities on the radar or to find where they lost their ATV, and overall it will be more logical for radar to be on the top floor instead of the signal processing room