no.
yes you can also catch them in soul silver.
no
try to catch your legendary. It varies on which legendary depending on what starter you chose.
You can catch Articuno in the Seafoam islands (Kanto), Zapdos at the Power Plant (Kanto), and Moltres in Mt. Silver (Johto).
a utra ball or a master ball
you have to catch Palkia(in pearl)orDialga(in diamond)
grovile
You are stronger of cource by pecy Jackson
Strong Pokemon like lugia, ho-oh and the three legendary dogs
After you catch them like any Pokemon they are saved on your pokedex and ready for use.
You go to the three caves and catch them.
you cant without trading. and which dog you encounter depends on which starter you choose. but you only get to catch one out of the three in the game by yourslef