Gaining levels:
Every time you complete a quest, you give the guild the same amount of xp. If you get 10.000 xp, the guild gets 10.000 xp, at no cost to you. Every time the guild earns a guild achievement, we get a number of xp. How much depends on the achivement. There is a daily cap on how much Guild XP we can earn. This is put in place to NOT promote bigger guilds over smaller guilds. With no cap, a guild of 500 people would reach max level in a week, where a 10man raiding guild would take months. More people only means it will be easier to reach the daily cap. Currently the cap sits at 6.246.000 xp per day. For the first few levels, that means we'll ding once every 3-4 days, provided we reach the cap every day. The cap resets at the same time as the Daily Quests and (not confirmed yet) counts from whatever amount the guild currently has.