Anyone lay their own concrete?

As said above, if you've never done concrete work before, get a contractor to do the pour and finishing. They already have all the equipment and know how to use it. You'll have 3-4 trucks lined up (depending on load limits in your area) and this is no time to be figuring out what comes next- you're on a time constraint to skreet, float and finish (paddle or broom, what's your flavor?); and by the time you rent all the equipment, your savings start to disappear. Plus, who knows what weather you'll be up against this time of year? For example, I finished pouring mine in the middle of a sleet storm that popped up out of nowhere... fun, fun. Thank you, National Weather Service. You can do the prep, gravel, rebar and such, but with that size pour you'd better know what you're doing with the forming- last thing you want is a breach while this is all going on. If you've never done it before, shop around to get the best price for the job, and see if they'll let you lend a hand. Learning lasts a lifetime.
And about that 4" floor- you'll want 6 if you ever decide to put in a hoist, or at least go thicker and have footings in the area where it will be installed.