For one and two: You should REALLY try History 3-3. Theres a trick to that stage to get...basically as much experience as you want until you decide to leave. After beating the dragons and the whole East section of the map, talk to the rock NPC on the top. He will tell you to hunt down a single monster (Hyena, Scorpion, or Lava). The trick is to NOT
hunt down what he wants. (ie. Say the rock wants you to hunt Hyena. Dont even touch a Hyena and instead kill other monsters). If you beat a room with the monster your not supposed to kill, youll get sent back to the stone NPC. You cant repeat that forever because the monsters keep spawning back everytime you enter a monster map. Just remember to avoid the monster the rock told you to get. In that stage, its not hard to get at least 10 loose boxes (maybe a few rares).
As for question 3, there IS no next Closed Beta. This game is a free MMORPG so the next stage of the game would be the Full Release.