Cynthia doesn't appear in SoulSilver. The Champion you verse is Lance. He has 3 Dragonites, a Charizard, an Aerodactyl, and a Gyarados.
use the pokegear
Yes
latious
You don't you have to use an Hm on a Pokemon
eevee
you get heracross or combees when you headbutt a tree
Use the Pokemon modifier AR code
you can't, but in kanto you can use the radio
Ecruteak
I advise you to use your map.
use a thunder stone on eevee
you get a poke ball and use it ._.