1. go play #1 endurance, use traps and stuff em with grade 2 orange gems to have some mana early. Even at level 17 you should be able to earn 4000 exp, which will push you 2 levels forward.
2. Those 2000-6000 mana after battle are not for you yet. Use dual lime/orange gems for towers, and pure orange gems for traps early, then red/orange gems for traps. And you should accomodate to more than one supergem running, especially once you will achieve the first one. Also do anger a LOT once you will have a supergemmed trap gem, especially red/orange.
Note also that a supergemmed pure gem has 100-120 firing speed at most, while supergemmed dual gem is able to get 225-279 (depends on grade of a gem and your "Recharge" skill). With zero in recharge ANY dual gem is capable to reach 225 firing speed, with 10 in recharge (way later) grade 6 gems and higher can be powered up to 279, while grade 3-5 can reach 222, that's due to different ways of calculating final speed of a gem and the cap.
3. (about enhanced pool skill) Currently it does nothing to the gameplay, and once you hit the cap with manapool spell cost, it starts to play against you.