Cant see it right now

I have collected several bottles of mana, but have no clue what they are for. They don't seem to be connected to the spells, which are on a timer. Anyone know?

I seems like I can win the map with no leaks, but not even come close to getting three starts. What is a good way of increasing my score? Less towers of higher rank?

... lost most, but not all, of my stars. I still had access to all the levels I had opened up though. Very weird. Is that supposed to happen?

My magical towers don't seem to fire at the slimes, but the description says it is their weakness. WTH?