Use galvanized nuts and bolts. Use at least 2 when attaching the joists to the posts, on diagonals to each other. Only use nails in the project where you install joist hangers. Use coated screws on the deck (assuming PT). You may have to check the code where the posts-to-concrete are concerned. (I'd consider using iron posts; not PT since you're going to sit on top of concrete. Again, check the code.) I'd set the bottom stringer up off the concrete a few inches on 'something' (depending on your taste). Don't forget to compensate the last stringer for the height differential. You still want the last step to be 9". If you don't raise the bottom, you run the risk of rot. And if you have rot, the owner may have to have the entire stringer replaced or 'hacked'. It's not worth cutting the corner if you know what I mean.
I keep reading that the posts won't be anchored to the ground very well. My $.02 says you should do what you have to do to make sure they are. You could end up in a law suit. And if you don't check the code for this aspect, I hope at least you look for other decks installed similiarly to see how they're anchored. My best to ya and hope this helps.