Please?
If you want to beat the game you can use this walkthrough: http://pokemonplatinum.net/v2/faq/
It explains what you need to do and where do you need to go in order to beat everything until the E4. This other page details some of the quests after the E4: http://pokemonplatinum.net/v2/news.php?id=231
I recommend you to beat the game and then get the Mystery Gift function activated (Serebii.net explains how IIRC) because Nintendo is going to be giving away the Member Pass card to get darkrai through Wi-Fi. I got the Secret Key in the same way but they stopped its distribution until next year I think.