i dont think you can
You can't battle Steven in Pokemon SoulSilver or HeartGold.
he will battle you in the kanto region but you need to have gotten the enigma stone to catch latias/latios he'll battle you in pewter city or saffron city
You can get latios after you meet Steven, and latias through the enigma stone event.
I don't believe that you get to fight Steven.
After you get your Hoenn starter and speak to Steven in the Pewter Museum, Steven will be in the Silph Co. bottom floor. He has a Beldum with a Dawn Stone to trade for a Forretress.
I don't really know. Although, my guess is he went back home to Hoenn.
on the top floor in a white building
After activating the no longer active Enigma Stone wifi event.
Yes you can. Don't believe anyone why says that you can't because I know for a fact that you can.
Eventually there will be an Engima Stone event in America. Once you get the stone, go to the Pewter City Museum and talk to Steven Stone, he'll take you outside and Latias will appear
Sceptile cannot be found in SoulSilver, but its pre-evolved form, Treecko, can be chosen from Steven Stone at Silph Co in Saffron City after defeating Red on Mt. Silver.
Steven isn't battleable in the game.