1. Cosmic-surge allows a cosmic character to regain a cosmic counter at the start of the recovery phase. This effect does not occur if the character in question is stunned or removed from play before the start of the recovery phase. It will only give only one counter back to the target character. As it stands, cosmic characters can not gain more than one cosmic counter at any time.
2. The 6 drop Destroyer states that you can reveal a character card named galactus to gain a cosmic counter onto that
Destroyer. However, it also states that this can only occur "at the start of the buil phase". For the Destroyer to recieve the benefit of gaining a cosmic counter from the Galactus reveal he would have to already be on the field at the start of the build phase. Sorry, you can't recruit the destroyer and then use his effect to gain a counter: you would be way past the start of the build phase by that time.
3. I don't believe you can use stardust as you suggested, but let me check.