Been there, done that.  Personally, I would try pretty much any other method of irrigation before going down this road. They are labor and fuel intensive, and not very reliable. IMO, it's worth putting up a pivot unless your land is just too irregularly shaped for it. We've precision leveled most of our land and furrow irrigate, which works better down here.

A gun will take one tractor to pull the reel, one to pull the cart out, and if you are laying hard pipe, one to pull the pipe trailer.  You will have to have a big, high pressure well which will take a big engine to pull.  

If you're set on getting traveling guns, do it right and bury an underground pipeline with risers at every pull set so that you don't have to lay hard pipe all the way every time you move it.  But I would still advise against going this route, unless you just don't like sleep.