is this 6 foot by 6 foot and 4 foot deep? Why so deep?
If I were doing this, I would do the 6 x 6 and only about 8 to 10 inches deep. I would improve my ground first, level it out, water it in and if necessary add some play sand. Then build my forms from 2 by 12's or good bender board. Then definately string my rebar. I would have it off the ground about 6 inches or so. Buy those plastic posts to keep it off the ground. Then rent a mixer and just mix my own batch on site with bags of concrete.
Should not be that big of a deal actually if you have the mixer.