I hope this is of some help. I am not a qualified spray painter but i have airbrushed for many years and have worked with spray painters. Alot of advice i have been given and adhere to myself regarding clear coats is to start the ratio about 70:30 thinners:lacquer (depending on the lacquer. Currenlty i am starting a bit thinker as the lacquer seems to be designed for colder climates and i live in stinking hot Brisbane). Hit the car with 2 coats of that mix then thin each coat as you go (2 x 80:20 then 2 x 90:10) until you are mostly spraying thinners. This gives the finish a much smoother feel and better gloss. Also to give the finish a much deeper look don't wash the pot out after you apply the final base coat but mix the clear in the pot so there is a thin mix of gunmetal grey with the clear. This will still spray on clear (provided you didn't mix too much base coat with it). I gives the metallic a deeper look. Also be sure to use high gloss thinners and not general purpose thinners to get a better finish. This is all assuming you are using acrylics as that is all i use.
As for your base coats and general prep. That sounds fine i guess. I never tack rag between coats myself but I see different approaches here so if you have been recommended that way the go with it.
The experts make painting look easy but it isn't so best of luck with it. I am about to embark on respraying my Sprinter...