Yes, once you shoot then, take out the cartridge and refill it the same way you loaded it up the first time.
I have never seen nor heard of a revolver airsoft pistol with non reusable shells. You should have no problems reusing them.
Yes.
Simply refill them, yes.
No.
No, they can not, do not attempt to mix real ammunition in airsoft guns.
Any spent plastic shotgun shells (hulls) should be reusable, as long as the brass is re-sized before reloading. Paper isn't recommended, and brass casings are practically non-reloadable.
It depends on the reason why they are
Yes, airsoft shells are refillable, being made of hard plastic and a hole to insert bb's in.
yes
Some shells hold up to 15.
Most sports stores will have them. Wal-Mart might have them. But E-Bay I know has them.
You cannot buy different sized shotgun magazines. However, I suggest getting a shotgun that takes airsoft shotgun shells. It will expand your options of bullet capacity.