Your mana shortage is mainly due to trying to keep your druids in leather gear. It's cool looking, but doesn't have the int and spellpower that cloth does. Don't use moonfire for trash, it's very mana inefficient. Stick with only the most efficient spells, like insect swarm and starfire; and wrath spam only when in trouble. These are only suggestions to keep from having to drink a lot, but it's most important to just have FUN! (But I guess that clearing faster could be funner.)