1. i don't understand the question.
2. yes, use a sharedobject
3. enable the cacheAsBitmap properties of mask_mc and bane_mc.
1. I mean are possible several masks at the same time?
yes, but you can't mask a mask and have it do what you would expect, you can't mask more than 1 object with the same mask and you can't assign more than 1 mask property to a displayobject at any one time.
if you want to apply mask1, mask2,.., maskN to bane_mc, you would use something like:
var parent_mask:Sprite=new Sprite();