Another thing I might have forgot to mention... New Amber Town is pretty much smack dab in the middle of the Viore Region, so the only direct route would be by plane. Travelling by boat would take days, if not weeks. Then there would also be the long trek from whatever port you came from to get your Pokedex, which is neccessary to challenge the Viore Pokemon Gyms and Contests, and the final events associated with them. Now, after getting that out of the way, to the new Characters:

[@Uccello] Accepted. And if you want Celebi, it's fine.

[@Leoven] Accepted

[@void liege] Accepted.

[@Dynamo Frokane] Accepted.

[@Ninian] Having Celes' guardian be Latias seems like a perfect fit.