yes... though it is very rare to find one
The red Gyarados is part of the game, but I did catch a Shiny Magikarp in Slowpoke Well.
Yes, you can get a shiny Pokemon out of an egg on any game.
Fight tons of Pokemon or cheat
everywhere but very rare
yes.zach does
Randomly when you run into a wild Pokemon it may have a different coloration that's a shiny Pokemon. Also a free shiny Pokemon is found in the lake of rage.
Yes, you technically CAN get a shiny magikarp but its not automatic. You have the same chances of getting a shiny magikarp as you do a shiny Pokemon from any other kind of egg. The parents don't automatically make it a shiny magikarp.
Latias is not available in SoulSilver
Keep walking in tall grass.
You transfer it from Heart Gold or Soul Silver.
pogi
According to Serebii.net there are 493 Pokemon in Soul Silver.
there isn't one.