Q&A for How to Get Hitmontop on Pokémon FireRed

The Day Care Center in Kanto only allows one Pokemon to be raised. It's the one on Four Island that allows two Pokemon to be raised at once.

Nothing. It is the game's way of telling you that it is not the best option. Normally the best combo is the same Pokemon. After that, the same egg group. This is why the game states Hitmonchan and Ditto don’t get along very well.

After you give sapphire to Celio you can enter the Cerulean Cave and catch the Legendary Mewtwo.

You need to get the Ruby, then you can go to Four Island after Bill upgrades your Tri-Pass.