i understand your pain...i am a pre register player before the game even start... and now i got 5x nat4* with Rm150 spending.. but i consider myself lucky lo... of course cannot compare those who are even more luckier one.. 

Lvling those mobs? fastest way is to lvl at the right most instance with the hardest difficulty that you can clear. which stage doesn't matter, they give the same exp.

I don't believe there are differences between summoning from Mystic Scroll and Crystal, so its best to save the crystal up to 750 to get the package deal from the shop. Unless you think otherwise, or couldn't wait for it.

First page got a lot more information about the game.