For example, can i trade my starter pokemon on Soul Silver to Diamond?
Yes you can. It is not like Pokemon black and White and the older games where you have to use the PokeTransfer Lab and only trade one way. The older games and SoulSilver are linked so they can trade and battle both ways.
Why, yes, yes you can.
No requirements, except that both games must have at least two Pokemon to trade.
you can trade any way within the fourth gen (diamond, pearl, platinum, heartgold and soulsilver)