Question.... do you have a pressure washer?
If you are not going to polish the car after then your goal is to minimize the amount of touches during the entire process.
If you do have a pressure washer then use that to knock off all the loose dirt first. Spray on your pre wash product (APC, Degreaser) then use a bug and tar soap and foam the car. let it dwell a bit then rinse off. Use your chemical decon products ( iron remover, tar remover) then rinse off. I had never use a rinseless wash to wipe down an iron remover or a tar remover but I heard others had. At this juncture, the vehicle should be 80 to 90 percent clean of debris and grime. Dry or blow dry the vehicle to prevent spotting if you dont have a water deionizer hooked up to your water source.
Keep in mind that claying the car with any clay medias could potentially mar the paint. The clay towel should be broken in by the time you are done with the windows. Clay the rest of your car with ONR one panel at a time. It is ideal to have a bucket of clean solution near by to rinse off the clay towel. Before moving on to next panel do another spray down with ONR then wipe. Spray 2 squirts of the sealant in a new towel and wipe down the panel then use another clean towel & "buff to perfection". To minimize any potential issues... I recommend doing this indoor.
To be honest... I simply dont like to use waterless wash on a dirty car. If you are using a power washer then you could skip the ONR claying process and just foam down the car with a good Lubricity car soap that has no gloss agent. Go to town with your clay towel then rinse down the car. Use your drying aid (Opti seal) and towels to dry as well as to seal your car.