Carb knowledge help needed

Im wanting to understand some carb theory and tuning knowledge ( holleys) and even though I have worked with many carbs (holleys) over my life I have never been "schooled" on the how it works internally.
The reason I want to understand this a little better is because I plan on going to a 2x4 tunnel ram sometime this year and I want to set up the carbs to be efficient when running on the street. I am thinking about using the one to one linkage setup. I will be using 2 holley 600 CFM carbs on a 408 which should have around 500 HP.
Im sure I will get many different theory's and thats fine because when tuning there are many different ways to get the best setup that will work.
First question is about a carb when idling. Is the fuel drawn down into the intake by the vacuum of the running engine? And if so, how does using 2 carbs effect that vacuum and does an idling running engine draw the same amount of fuel from each carb as it would if it were a single intake carb or does it draw less fuel from each carb then if it were a one carb setup?
When tuning the carbs how many use the engine vacuum gauge in order to tune the carb? Advantages vs draw backs?
When making adjustments using the air screws in the front just under the bowls will it only effect the fuel/air during idle?
In order to change the fuel off idle I need to change jets? Squirters? Or is there another way?
I know I can change ramps on the linkage and I can make changes to the accel pump adjustments but I am more curious about how and what the passages do and how I need to use the circuits for a better setup.
Thanks for any knowledge you can pass on.
Rod