It is FireRed that needs the Sapphire & Ruby Crystals :) x
It's not possible to find Sudowoodo in Pokemon FireRed. You will need to trade for one from a Pokemon Emerald game-save.
You can't catch it on Firered you can only catch it in Emerald
There is no emerald to trade between firered and emerald you need wireless adapters.
You cannot get umbreon in firered you need to have ruby, sapphire or emerald give you one or take the one from Pokemon colosseum.
caves
Yes, Pikachu is able to learn Dig. It can learn Dig through the use of the Dig TM, which you can buy at the Cerulean City Poke Mart.
You can buy them in firered then trade them to emerald.
In Pokemon FireRed and LeafGreen, Diglett can learn Dig at level 17, which is a nice and early level for a good move.
It is FireRed that needs the Sapphire & Ruby Crystals :) x
It's always easy to use escape rope, or DIG, or TELEPORT.
you need the pokeflut
You'll need to trade it from Pokemon Emerald.
You need to find the two passwords...
you need to trade from Pokemon leafgreen or firered
eevee and staryu
Neither pokemon can be obtained in firered you will need to trade both from Ruby, Sapphire or Emerald.