Re: AIO, I think the first thing I'd do is read the instructions. I just looked at my bottle of AIO and it said nothing about adding it to water. It's prolly best to apply it to the painted parts of your car only.
You can certainly clay your car if you want to. I imagine you car could use some claying if its never been waxed but that's a guess on my part.
I think Mike Phillips has written about Cleaner Wax and Gold Class recently so you might want to search his posts for more info. Mike works for Meguiar's, BTW so he'll know the diffs between the products. You could also call Meguiar's Tech Line and ask, 1-800-347-5700.