Hey Kazzarat
For hunger, you don't regen how/mp/sp as much as you get hungrier. Eating food (which can be created with a spell, bought from shopkeeper, or found from monsters) both reduces hunger and increases the amount of HP you regen on the next regen. You're right that this isn't documented anywhere, I'll make sure info gets added for it in various places!
For defense stats on gear, they don't effect crit chance at all. The defense that armor gives goes into some equations when you are attacked to determine whether or not you take damage and how much. It's also based highly on the attacker's weapon and abilities. The higher the defense, the higher chance you avoid damage at all and also the less damage you take when you don't avoid completely.
Mining is all done in the underground areas, which can be entered from the main towns as well as the contested land and a couple other spots. There is a dark spot in the map for their entrances, when you find them, they look like a dark hole mostly surrounded by a metal gate. Thanks for bringing this up, I'll make sure we get the maps updated to show where they are and add some info about the underground/entrances to the mining web page!
For stats: strength allows you to wear heavier armor, wield heavier weapons, swing heavy weapons faster, and increases physical damage. Dexterity increases your probability to physically hit opponents and also decreased your probability to be hit by opponents. Vitality increases your max HP, increases your hp regen, and slightly decreased damage taken. Intelligence allows you to learn better spells, increases your cast probability, and increases your magic damage. Magic increases your max mp and increases your mp regen. Charisma is needed to start a guild and also slightly increases your luck for finding items when fighting monsters. Again, this was missed in documentation and I'll make sure it gets added to the website and probably the help pages!
Thanks for posting all of the questions, they pointed out some oversights that will definitely help people once we updates out in the next couple days! Let me know if you have more questions!