There is an in game encyclopedia. I often will internet search to look specific mechanics up though. E.g. pathfinder kingaker wiki.
Character creation can be a bit daunting. There are ~5 precreated characters if you want to use them. You can also respec in game too (entire race/class for main). First three uses are free, then scaling gold cost.
You will want to level "persuasion on main character. Try and cover the other skills through out your party. Esp perception and trickery and the lore ones.
Primary classes not available as story companions
Low to mid casters definitely favour crowd control and utility buffs/debuffs over raw damage. Some can switch their prepared spells for the day (clerics, druids, wizards ertc) versus the spontaneous casters that know fewer spells but can cast them more often and flexibly (bard, sorcerer etc)
The dlcs are pretty good, esp to play around with more party options
Varnhold is a mini campaign that imports into the main one.
Beneath the stolen lands is a great little character/party tester of quickened leveling of multiple custom parties through condensed combat.
Wildcard adds an array of useful tieflings and the complicated but pretty cool kine class.
The turn based is solid, esp for learning the game or harder smaller fights. Can freely switch back and forth on the fly
I don't use mods myself due to external hassle and patch versions. There are many options tho, not sure if all updated.
Don't lay above normal. Set kingdom management difficulty to easy. Be aware that at points you will meet enemies you are not currently equiped to deal with (cough swarms)