Steven will be in Silph Co. after you beat Trainer Red(Get all 16 Badges,Elite4) on Mount Silver. He will give you 1 or the Hoenn Starters at lvl 5.
Only in an event.
See related link.
The Embedded Tower.
In Pokemon SoulSilver, Marshtomp evolves into Swampert at level 36. See the link below.
By using the TM Flash
You can trade one from another game, in soulsilver you can find a trainer with a chimchar, then go to the GTS and evolve it.
You can find them in tall grass and catch them, so yes, you do get to see them.
No, neither did i :|
No You dont
it allows you to be able to see the leagendary lugia
See related link for details.
beat Clair then go see professor elm