As long as you dry it off well, it should be ok. My car has been sitting with bare metal for a while now, and it suprisingly hasn't started rusting. Just make sure to use dish soap, like Dawn, Joy, Palmolive, ect... do not use car wash soap. Car soaps include silicons to coat and protect the paint, but your paint won't stick over the top. Yes, you will be spraying it off with a hose though.
If you wash it with towels, you would be using the prep solvent. You basically poor a bit into the towel (make sure the paper towel doesn't leave fuzz or dust, you'll probably really want a roll of the blue shop towels) and start wiping in straight lines along the car. Repeat this until the prep-solv doesn't pick up anymore dirt.