platinum is better because it has more content
No you cannot trade from Sapphire to Platinum. The closest thing that you can do to that is migrate from Sapphire to Platinum.
yes you can migrate from any of the emerald Sapphire and the other on to platinum
Yes, you can get the Gemstone Ring: Platinum Oval Sapphire & Half-Moon Diamond Ring with a ruby instead of a sapphire.
You can't get him in platinum. You have to transfer him from a Sapphire/Ruby/Emerald.
Yes.
buy them
You must transfer it from sapphire.
You can migrate it from Ruby/Sapphire/Emerald. migrate it onto platinum from leafgreen firered ruby emerald or Sapphire or use the cheat. signed:pokemonexpert
migrating him from ruby or sapphire!
Trade from Sapphire/Emerald.
You have to migrate it from Sapphire or Emerald.
You can't catch rayquaza in platinum unless you migrate it from ruby, sapphire or emerald.