I use the Simoniz Universal Foam Blaster available at Canadian Tire. For soap I use the Chemical Guys Mr. Pink. The process is as mentioned above. Wet the car first then apply the foam, but then I use a micro fiber wash mitt to wipe down the entire vehicle then rinse off the soap. I then pull the car into the garage out of the sun and dry the car with micro fiber towels.
I use my pressure washer to wet the car, apply the soap and then rinse it off. I use the 25 degree nozzle so there is not a lot of pressure on the finish but more than enough to get into the wheel wells or the wheels - with brake dust issues- and get them cleaned up.
As for soap consumption, 2 cap fulls into the 1 litre blaster bottle and the rest filled with water is enough to do both my C7 and my wife's Caddy XT4 and the suds are unbelievably thick. Looks like the car was in a snow storm. For pricey vehicles that run premium gas, a few extra cents for decent soap regardless of how much you use, is not really an issue in my opinion.
From experience what they show in the ads - apply the soap, let it sit for a few minutes and then rinse does NOT work well. It leaves streaks and water spots. Wiping with a mitt, rinsing and then drying in the shade of a garage is the best approach for me.