Obtaining all of Professor Oak's Pokemon can only be accomplished via Cheat Codes.
You will have to trade it from other pokemon.
Yes migrate them.
you have to trade them from other Pokemon games
No but i think you can trade it from other Pokemon games
yes like in all other Pokemon games there is a Pokemon center
impossible unless if you trade it form Pokemon leafgreen or other related Pokemon games (except DS Pokemon games) . in other words it is a Pokemon version exclusive Pokemon like growlithe (firered) and vulpix (leafgreen)
you can get Pokemon that are not in the other version
There is no "best" Pokemon because every Pokemon has its own weaknesses and strengths against other types of Pokemon,
Skitty as well as other hoenn Pokemon cannot be found in firered all hoenn Pokemon must be traded to you from ruby, sapphire, emerald, Pokemon colosseum and Pokemon xd gale of darkness.
Trade masterballs from other games to firered.
Get the other 249.
Light Mountain is not an existing location in Pokemon FireRed. Light Mountain doesn't exist in any other Pokemon media including the movies and comics.