Anyone lay their own concrete?

You must be a glutton for punishment if you want to try that with no prior experience. I've done some concrete in the past, way way past when I was a much younger man. Believe me, concrete work is a YOUNG mans job, in the case of your 21 yard job, SEVERAL YOUNG men's job.

Just finished up a 72 yard concrete job yesterday on my 40x80 post frame barn and it took all told, SEVEN young men from age 16 thru 25 (and of course, me supervising!) I couldn't be happier, they did an absolutely great job, almost perfect as far as I can tell, and I'm pretty hard to please. (Concrete hardly ever comes out perfect, no matter how much you plan and prepare.)

You are much better off paying someone with good EXPERIENCE to do the job for you. Just my opinion of course!