I apologize for the late responses...
@ TheMatias -- Yes, STR affects your P-ATK, so higher STR means higher base damage. Crit DMG raises the amount of damage done by a critical hit, while Crit Rate increases how often you make a critial hit. ACC increases your chance to hit. Luck increases your Crit Rate, M-Crit Rate, and ACC.
@ Tremphthon -- Class Expertise is actually now called "Class Talent" (updated) where you can spend Knowledge Points to customize your class.
@ Rubix100 -- CP is earned by killing monsters and it is applied to your current class. Therefore, each class has its own CP to spend on skills. As for silver/gold, it depends on how many repeatable quests you do and how much you spend along the way, but after level 30, skills begin to get quite expensive, so it will be harder to maintain multiple classes. Choose the most important skills to level first, then work on the rest as you can.