The two darkrooms I have built have been of a long and narrow "galley" shape. Enlarger and darkroom sink along one long wall, and and eight foot counter-top along the other, with space for dry mounting press, light boxes, and film loading space. It's only six feet wide by 13 feet long, leaving me maybe a 22 inch aisle down the center. It feels cozy and efficient for me, with zero waste space. If two people were going to work at the same time, that center aisle would probably need to be at least four feet wide.
In your case, you want to add a darkroom onto the house. This sounds like new construction, not just a room walled off in the basement. Depending on the space available, perhaps a galley type design would work for you, by placing the long wall agains the exterior house wall. If you made it 8 by 16 feet, you should have room for all those enlargers (well, maybe 8 by 18 feet), and the new construction still wouldn't stick out into the yard too much.
In between the hot and cold water, you will want a mixing valve to regulate temperature. If you get a regulator valve, be sure and get one meant for low flow rates, like maybe a quart or two a minute. One meant for higher flow won't do a thing at the low flow of an amateur darkroom!
An under the counter refrigerator is essential for beer. A second one for film and paper might be considered, space permitting . . .
Lay it out on paper with rectangles cut out to move around representing the sink, counter, enlargers, etc. As Wilbur and Orville said, "If it works on paper, it'll fly."
Don't forget the doorway. And the door needs to be light-tight. Oh, and if you have enough space, a light trap is a wonderful luxury! You can walk in and out with no need for a light-tight door. Aids air circulation, too.
Good luck with it!
