Elite four and Ruby/Sapphire Trades

Hmm, well, align your Pokemon to take on the Elite Four by type advantage. I believe they go in this order: 1.Lorelei (Ice/Water user-Zapdos better have good Electric attacks); 2. Bruno (Fighting/Rock user); 3.(forgot the name)(Poison user); 4. (forgot the name and type favored); 5. Rival-Pidgeot, Rhydon, (in your case,Blastoise, at level 63),Alakazam, (in your case, Arcanine and Exegcutor).

My other advice: 1. Get all your Pokemon at least level 50.
2. Get yourself a strong Psychic-type to blast at the Fighting and Poison users.

As for the Ruby and Sapphire, you don't get to do that quest until you've defeated the Elite Four. Once you do, though, go to One Island and talk to Celio. He'll make it so that you can travel to Four,Five,Six,and Seven Islands. I believe the quest begins on Four Island.

As for Deoxys, I don't think you can, but I believe if you can, it'll be on Seven Island, I think.

Well I suggest that you get dragonair to evolve into dragonite at lvl 55 and then your zapdoes is good for the first of the elite four if you teach it thunder, your charizard and articuno for bruno(and if you get dragonite teach it these moves: wing attack, surf, blizzard, and outrage at lvl 61 and the fourth before outrage is a free choice), for agatha who uses ghosts/poison I advise you get a phychic for her as it will work marvels on all her Pokemon,for lance he is associated with a gyarados, aerodactly(srry about spelling),and dragon type Pokemon this is where zapdoes(for gyaradoes)and dragonite with surf and blizzard(and if you got outrage great)use blizzard/ outrage on the dragons although be wrned use outrage aparingly for areodactyl will come up and use surf on it,and for your rival that assortment right there should do you.