I loooooved my set up with stalls to runs to sacrifice area to pasture. It worked SO well and made day to day operations SO easy. There was a 12’ overhang off the barn that served the runs, and if we’d stayed there longer, I would’ve installed an auto water in the sacrifice area.
Inside the barn: light. Light everywhere. Outlets, but also work in as much natural light as you can. Translucent panels are awesome–we did those in the gable ends and it made the barn SO light and airy. My barn now has a loft, so panels in the gables doesn’t work, but we replaced the big sliding aisle doors with windowed ones, and that helps a lot. I’m considering adding clear panels over the dutch doors, too, to brighten up the stalls.
For your outlets, consider how you’re heating your water in the winter (if you have winter) and CONFIRM that outlets are in places where cords can reach. It’s so frustrating to be a few inches short.
Two banks of lights down the aisle, offset to each side, is better than one bank down the middle.
The option to turn on lights over each stall is nice, but at least give yourself a night light–one light you can turn on independently–so you’re not lighting up there whole barn unnecessarily.
Even if you’re not installing fans right away, have the electrician wire in where they’ll go, so you can add them easily later. Consider doing that in the stalls and in your sacrifice area.
Setting it up so you can power wash the entire inside is really nice. Seal your tack and feed room somehow, and grade the aisle slightly away. In my barn, water flows under the wall into both rooms and it’s a huge pita.
For hay storage, consider making it accessible to a skid steer, as more hay is being put up in big bales or bundles. If it’s got to be hand stacked small bales, that can be limiting.