Yep pretty much everything he said. ^^ We're here to help! And meth is fascinating. It would be very good for you to learn your system well. It's fun to add on to it and make tweaks. It's surprising what a difference a little tweaking can make.
The shops statement that you do not need a CV or solenoid is way off. They are correct in saying that you don't see vacuum where your nozzle is, but there's nothing holding pressure in your lines! You don't need vacuum to have water pour out of a line. Gravity will just do its thing without a CV. And to clarify, yes a Check valve and Solenoid basically do the same thing. Solenoids respond a little quicker because an electric current tells it to crack open whereas a CV is all pressure based. Most have a cracking psi of somewhere around 15 ish.. so the response is a little delayed.. nothing you would ever notice though. I had nothing but check valves on my system, Which was a dual nozzle set up where one nozzle was after the throttle body in vacuum, and the check valve did just fine.
To help you understand, a check valve works the same as placing your finger at one end of a straw with water in it. as long as your finger is sealed over one end, the water wont budge. however pull your finger off and the water immediately pours out. So your system is a fingerless straw right now. There's nothing holding pressure in your lines! I'd suggest just starting with a Check valve. Your system is basic, so it will do the job.
Start spray and full spray, mine was set up at 4 psi start and max at 14. And i was flowing a lot more than you are!! These mk7's have a bigger turbo than the mk6 and a lot more power, so you're definitely not flowing too much, or starting too soon.