I too would avoid the Dawn unless you are going to Zaino ( which you are not). I normally start with a wash if necessary and then start the prep. I alway use enough lube when I clay so streaking is not a problem, polish ( for deeper marring), SMR, GEPC, I sometimes add in a Mother's Sealer/Glaze step and than protect ( In my case EX followed by Souveran, P21S, and Super Shine). I also QD ( non-carnauba) after my polishing step prior to SMR'ing. This removes any microscopic polishing agents left on surface and also allows me to evaluate the finish.
If you feel you vehicle needs a wash during this prep just use your normal car shampoo. :wavey