Ahh… This is an area I have much experience with. My husband and I built our house/barn combo by ourselves and did plenty of research ahead of time. It helped that my husband (an electrical engineer and lighting specialist) works with civil engineers and architects. But we did all the work ourselves.
These are things that we did and love. But first let me preface this by saying when it comes to wiring and plumbing it is MUCH easier to rough in things that you may not want/need now but you want in the future.
Invest in a small water heater for your wash stall. When building this area I would rough-in for radient heaters if you show or need to wash a horse in cooler temps. We used caned fixtures down the center of our aisle. My barn aisle has excellent lighting because of this and it also looks good. We also used canned fixtures in the wash stall (these need to be rated for wet usage). We have ceiling fans in the center of each stall so that is something that needs to wired for. Each stall has a separate light switch for a double spotlight socket which is mounted in the front of the stall. If needed you can put a heat lamp in the spare socket. The switches need to be far enough away from the stall door so that the horses do not play with them.
Make sure you put in as many outlets in as necessary, Only those that come in possible contact w/ water need to be GFI rated (like a receptacle in the wash stall).
Make sure that you put in an outlet and have space for a fly system (one of my favorite items). We built on a slab with textured concrete floors. They are great. No slipping problems here. Stall are matted of course bu aisle is the easiest to clean. For plumbing make sure they use copper pipes and insulate your pipes. One of the nice things we did was when we pipped our automatic wateres we put in a shut-off valve to each one with an access panel in the inside of each stall. So if anything happens to one of the wateres or if I need to clean one I can shut off water to that individual waterer and the rest still work!!
