I looked again at your drawing and I'm not sure how long you plan to be in this house or how much time you plan to spend on this hobby.
I guess my question is about your initial concepts. Since the plumbing and electrical are going to be your main costs and hastle I really think I would be building the darkroom where the drying and display room is on the other side of the furnace.
There you have room to grow and expand. If you spend the money for the plumbing and electrical and find that you are too cramped, which you are, you may be sorry in the long run.
The length of pipe for plumbing is not that much and a sump pump for drainage is also not that much. What costs is the labor and facets and those prices are fixed.
I guess what I'm saying is that, in my opinion your darkroom should be your first priority, and the other areas can be anywhere.
So my suggestion is that you maybe, rethink the location of your darkroom to make it a room you can be comfortable working in and a room you look forward to working in as well as a room that can grow with your experience.
Just a suggestion.