I'm looking at your "Current Layout" drawing. Do your bathroom water supply and drain pipes come up to the second floor through an exterior wall? If so, that's verbotten where I live cuz of the possibility of the pipes freezing. I'm guessing it's not a problem in Kentucky cuz it doesn't get cold enough for long enough for that to happen.
If it wuz me, I would have a bathroom consisting of two separate rooms with a lockable door between them, and a door to each room. One room would have a toilet with sink and the other would have a shower/tub with sink. You need a sink in the toilet room to wash your hands. You need a sink in the tub/shower room to shave before showering. That way if someone wants to use the toilet, they can even if someone else is in the shower and vice versa. You still need access to the shower from the toilet and vice versa, which is provided by the lockable door, but keeping the toilet and tub/shower in separate rooms allows both fixtures to be used simultaneously and minimizes toilet tank sweating. That also means you need a ceiling fan in both rooms.
If you find yourself running any new piping, run 3/4 inch copper hot and cold water supply pipes instead of 1/2 inch. That's cuz, provided there's no bottle neck upstream, a 3/4 inch pipe can supply full flow to two 1/2 inch pipes, so you can flush the toilet without having an appreciable change in the shower temperature. And, I'd try to get those pipes out of the exterior wall if possible.
If you have time, maybe go shopping for an expensive recreational vehicle or yacht. The space inside those things has to be designed for optimal utility because of the very limited amount of it. Then see if you can work any of those ideas into your floor plan to give you more room with the same optimal utility.