Hi and welcome
I think a lot in these 2 threads can be a really good help to a new mixer.
To answer your first question i would say that there is no given percentage on flavors to a mix besides you might not wanna go over 20% by much. Most mixers i know of try to keep the flavor percentage under 20%.
Me myself live by the rule that less is more and i try to keep my percentages as low as i possibly can.
In short it depends on the concentrates your using. One example is flavorart…many report 4-7% is a better desired range with 10%'ish is the max give or take 1-2 depending on the mix.
Read the average percentages and notes and if 6 people say use only 1% start with 1%
They all are different animals. To mix well, starting at 1% or 5% with everything will not yield a good result.
Examples:
Coffee Flavors: Some coffee flavors like Caramel Cappuccino or Cactus if you use more than a half a percent your first tank or cloud could throw you out of your chair.
Vanilla Custard Capella V1: You need between 5% and 8% for some people to get what they want out of it. So read the notes for everything and use what most people use for a starter percentage.