If by four post lift you mean one of the drive on style, with two large flat surfaces that raise with the car, they are really only good for oil changes and transmission work. Without costly upgrades, they don't lift the vehicle off of it's own wheels, so brake and chassis work is ruled out. And even with the optional little lifts, chassis work is hampered by the "ramps" being in your way. They are also only suitable for lifting average sized cars and trucks, not very versatile for other work. A two poster can work as a hoist, can lift pick-up beds off of frames, can lift bodies off of frames for that matter (useful for restoration projects). A two post lift with adjustable arms can often lift smaller vehicles also, golfcarts, Smartcars...

There's a reason the pro's use two posts (except for alignment racks), and a reason that homeowners looking for extra parking use four posts.

Definitely put the compressor outside. And plenty of drying capacity for the air you'll be using.

The shower was another good idea. The safety features are great, and the convenience is great. Also a big plus with the wife. Or a big plus for you if the wife kicks you out.

Someone mentioned internet. Another must have. Consider a small "office" area that's sealed off from the other parts of the shop. Computers and printers are pretty much part of the toolbox these days, but don't care for the same enviroment. Also a good place for the fridge you mentioned.

The exhaust extraction fan is also a good idea. As is some sort of large fan for clearing the whole place out. We have swamp coolers for our shop, and they will flush out the air fairly quickly, but something like a whole house fan might be good. Smoke/odors/fumes can make a shop unworkable, or even dangerous.

Concrete pad outside, leading up to the doors is also a must.

Plenty of good ideas.

Oh, and a dog. You need a good dog to go in the shop. That way you have someone to complain to when things go awry. Otherwise you'd just be out in the shop talking to yourself like an idiot, and no one wants that.

MV