You can change Rotom's Form by interacting with the cardboard boxes in Professor Birch's laboratory on the bottom right corner. This will also give Rotom a new move as you change its form to what you want it to be.
No, you will need to trade for them or transfer them via Pokemon Bank to get them in Pokemon Omega Ruby and Alpha Sapphire.
Nowhere.
No. Regigias is only available in in gen 4 and up. You can catch regigigas in Pokémon omega ruby and alpha sapphire
In Pokemon Omega Ruby, Latios can be found in Southern Island after obtaining the HM Surf and going to Route 123. To find Latias, you will need to get the Eon Ticket to fly to Southern Island to get her. Pokemon Alpha Sapphire has the same methods, but with the opposite Pokemon.
in a cave somewhere in the dessert is where i rember getting mine
Rotom cannot be found in Pokemon HeartGold or SoulSilver. Rotom must be traded or obtained via an event.
you can only find it during swarms
I'm think in the woods at the start of the game.
Pokemon ruby's version IS Pokemon ruby.
To receive Rotom on Pokemon Heart Gold and Soul Silver you must trade it from Pokemon Diamond, Pearl, or Platinum.
You will need to trade for Weedle or breed Kakuna. Kakuna can be found only in the Safari Zone in Pokemon Alpha Sapphire and Omega Ruby.