I built my own slab, with about the same proportions. Here is what I did, maybe it will help in deciding what you should do. Our slab has been around for about a year with no problems.
1) I dug an 8'x9' hole, 8" deep.
2) I then dug 1' "footers" an extra 4" deep all around the slab. This will, supposedly, help decrease slab movement over time.
3) Tamped the ground with a hand tamper, $8 at home depot.
4) Poured 4" of drainage rock. Tamped it by hand.
5) Spread some plastic sheathing over the rock.
6) Made concrete forms out of wood, made sure they were square.
7) Built a mesh out of 1/2" rebar, every foot. It came up to 6" from each edge of the patio. Found that cutting rebar by putting a metal-cutting blade on a mitre saw is fun, and sparks are mildly painful.
8 ) Bought a bunch of "rebar holders", which hold the rebar up a few inches, otherwise, the rebar will sink in the wet concrete.
9) Had a concrete company deliver mixed concrete, which me and some friends wheelbarrowed to the slab. Had it aerated and had fiberglass support put in. Ask the local concrete dleivery people, they will recommend what to use for the slab in your area.
10) Smoothed it and screeded it was a long, straight 2x4.
11) Kept the top wet for the next 5 days. This involves watering it and keeping hay or newspaper or something else on top to keep the top from drying out.
12) knocked down the wooden supports.
No expansion joists. Digging and leveling the dirt was, by far, the hardest part. The manual labor was done over 2 weekends (1 weekend digging, 1 weekend for rocks and forms and concrete). We took our time. I'm sure it could have been done in a single weekend.
Look to get drainage rock in bulk and not by bag, you can save a bundle and use the extra is different places in your yard if you like the look.
Hope this helps!
-Ed
