Putting up a small barn.... suggestions?

My family is looking at putting up a barn and arena on our property, and I'm still pretty unsure about how much space we'd need.

The basic things that I want for the barn are:
- a minimum of two roomy stalls
- a tack room
- a run-in space with room for all six horses to get inside without a fight. I want the run-in area to be indoors, so that I can shut them all in if I need to, but still be well-ventilated and such. (I was actually thinking something like a big open space with big doors at both ends that can just be left open.)
- a small office-type area, with a restroom
- and some kind of wash area (though I'm not sure if I want it indoors or outdoors)
For the arena, I want it big enough I can practice barrels in it. I'm thinking on modeling it after the arenas at the local fairgrounds, since I like that design.
I wouldn't mind some kind of covered area off the side or something to park the horse trailers in, too.
I want to put mats down in the stalls, and I've had people suggest putting limestone under them. For the alleyway, I'm torn between a textured cement (texture to give it some grip, so it's not slippery), or more mats. The run-in would probably be sand or dirt floors.

My horses range from 12hh to about 15hh, if that makes a difference. and the plan as of now is to put in a pole barn of the size we want, and then add stalls/rooms/etc inside of that, a bit at a time.
A friend of my mother's has agreed to help out with the construction and planning, but he's mostly just done homes and a few garages. My dad has built barns before, but only for cattle. My mom is an electrician and, between both my parents, they can do any wiring and plumbing that's needed. We also have access to an awesome group of guys who can and often will weld up anything we ask them to for the cost of a good steak dinner. So we're saving a lot of money that way.

My questions are:
How high should ceilings/doorways be in the horse areas?
How wide should doorways be? (I've already heard that main doors should be wide enough for a person to go through with a horse on either side...)
How wide should the main alleyway be?

Also, to those of you who have a barn or frequent one, what are some of the features that you love/hate/couldn't do without?

Thanks in advance for any help at all!

Wow, wish I had your available work force!!!!

Our barn is a raised center isle. The ally is 16 feet wide and 18 foot tall. The stalls are 12x12 have 12 foot high ceiling at the lowest point. Each stall has a paddock of 24 x 12 with access for escape from the outside. We have a tack room and hay storage for minimum 168 rectangular bales inside the barn. We have a separate hay barn that holds a years supply of hay... I believe that is something like 24 x 48? Will hold around 600+ same size bales.

I wouldn't be able to make a run-in large enough to hold all horses, the lowest will always get booted out. Think about a couple run-ins.

A good sized arena should be minimum 120 x 200
Our horses are only in when the weather is very bad - if they want in, most times they don't. We do feed each in their own stall however to ensure they each get their amount of hay or special requirements, fly masks and look over whatever...and then they are turned out until next feeding.

Think about your center isle or alleyway - It's very nice to have the room to bring in a vehicle out of the weather and still have working room w/horse and vet, farrier etc.

I have watched so many friends build barns and everyone of them made them too small. Always go a big bigger then you think you need. Instead of 2 stalls do 3. You just never know and its much easier to do it now then add it later :)