There are a couple NPCs in the game that can trade Pokemon with you. They are:
There's a man outside Diglett's Cave along Route 2 that will trade Mr. Mime for Clefairy
A trainer on route 5 who trades Cubone for Machoke
Traders on Route 11, 18, and Cinnabar Island. You can obtain Dugtrio, Parasect, Rhydon, Dewgong, and Muk from them, but they are easier to catch on your own.
Yes you can trade Pokémon between two Pokémon Yellow games.
Meowth is not in the wild in Pokemon Yellow. You have to trade to get it
No. They are different generations, so they can't trade.
You cannot trade Pokemon to Pokemon Colosseum, but you can trade the Lugia you catch to Ruby or Sapphire.
yes
Pokemon Yellow does not have meowth and it can only be obtained by trade.
no
One can trade in Pokemon Yellow via link cable. Two Gameboy consoles can be connected via link cable and Pokemon can be traded across Pokemon Blue, Red, or Yellow.
The third pokemon center
You can't
Trade, neither Electabuzz nor Magmar are in Pokemon yellow
No.