Completing the Hoenn Dex in RSE does get you a GSC starter. The one about Prof. Birch is false.
Jirachi is only
available from the Pokemon Colosseum bonus disk, or a cheat. All the other legends are obtainable through cheats or Nintendo events.
The tickets are distributed at special Nintendo events, but not anymore I think.
I hope I answered your questions, you can look at the main site, it usually has all the answers