Hi and welcome to the forum,you will find answers to all your questions here,and we are all very friendly.
First of all,don't measure in drops,its not accurate.
Use a syringe or a graduated measuring cup that's used for medicine,far easier and more accurate.
I use this calculator for my mixing and i find it works well. http://www.todmuller.com/ejuice/ejuice.php
Mixing is all about trial and error and once you find the right way for you it is easy.
Good luck,any thing your not sure of just ask,we are all here to help each other