DPP>HGSS trades.

I'm guessing you can do it at any time, with the spiky-eared pichu event and stuff, but I want to make sure.Can you trade from DPP to HGSS form the beginning, or do you need to do something like beat E4 to be able to?

I would assume you need the national pokedex like the other games in the series before trading, which might mean that the current pokedex type needs to have all seen/elite 4 beat/etc.

I would think you'd be able to trade, hopefully. However I can't find out because every time I connect to Wifi to trade, it instantly freezes with a blue screen and error message.

You can trade them from the begining i think on the second floorfor wifi you need to have the first badge

You can't trade pokémon you haven't seen in game.