That's gonna hurt doing that much clay with a hand tiller. What's on the ground right now and has the ground ever been turned before in years past? I would spray to get a kill o fhte grass, will make the tilling much easier without the roots killing you. Wait for the rain to get the ground damp and then let it dry a bit before you try to till, then get the ground worked up as best you can. If you could rent a tractor with a tiller or something bigger it will make the work go much faster, but if you can not then just make use of what you have. For clay your hand tools will be almost useless.
Good thing about clay is it usually doesn't need limed. spread some fertilizer, get your seed in and hope for rain.