I'll help you out.
Mine is pretty small - about 8' square.
When I bought the house, it was the laundry room with the hot water heater. I moved the washer and dryer out and put in a utility sink.
I lived with the giant water tank in the corner for two years and then moved it out to make room for a 65 gal QT tank.
Here is the upper section
My sump is a 90 gal tank.
And the QT tank where the heater used to be. My RO system is on the wall to the left.
I have no floor drain in the room, but there is one about 8' from the doorway, so i can sweep most of it towards the drain. Plus, there is a little slope to the floor that will get a major flood headed in the right direction.
I sealed between the base board a floor with silicone to keep any water in the room.
I have no specific provisions for humidity, but this is in my basement/garage so I just leave to door open most of the time.
If I where building a new room from scratch 8'x12' would be a comfortable minimum. And if it was within the main living area of the house, I would definitely have provisions for a heat recovering air exchanger and or a de-humidifier. Orient the room along an outside wall for more flexibility with cooling options.