in silver/gold after you get to the seand city but to trade between gold/silver and red blu yellow you have to get to goldenrod
Yes as long as you are trading only Johto and Kanto before you acquire the National Dex.
yes as long as you can get to the uostairs part of the Pokemon center
You can't send the Pokemon directly from Pokemon Emerald to Pokemon Heart Gold but you can migrate your Pokemon from Emerald to Pokemon Pearl, Platinum, Diamond and then trade it to your game Pokemon Heart Gold as long as you have a friend with a DS(Dsi)
Time capsule... Pokemon / moves from Gold / Silver / Crystal and newer do not transfer back though. So the answer is yes. It is a long time before the capsule is available though just as a fair warning. You can transfer all Pokemon TO G/S/C and newer, and if it existed then you can trade it back (Pokemon like Ghastly and Rattata)
You can trade from Sapphire anytime. However if you are trading to or from Leaf Green, you have to have beaten the Elite Four first, before you can trade with Ruby, Sapphire, or Emerald.
long because i traded and it took ages
you must trade it to platinum pearl or diamond and level it up by the moss rock. as long as you trade it back to the original trainer afterwords, it wont act like a traded pokemon, so make sure your eevee is from your heartgold game.
Depending on what Pokemon it changes
anywhere just as long you are inside the Pokemon centre
you bring out this long cord and plug it in to the game boy
There isn't sorry you have to do it the long way round
its a long term process, first, you have to get the mist stone in Pokemon blue, ect, then you have to trade the Pokemon to silver or gold, ok? In silver or gold, you complete the pokedex to get the time machine where you can then trade to Pokemon leaf green or fire red, and then u transfer Pokemon to diamond or pearl! (the mist stone evolves starter Pokemon into pokegods) :)