I hate this stygmatism against the chaos alignments. Sure, I'm a little crazy, but not enough to murder my allies or run off on my own.
The chaos alignments are so misjudged,(as much as evil typically is)
Chaos doesn't represent pure unadulterated chaos, it represents freedom of choice and the embodiment of a free spirit!!!
Which is ironic for Hastur seeing that all his followers have seen the yellow sign one time or another- meaning they are basically all unwilling followers to the God. And under his control if you really want to get deep into it.
But honestly I'm picking Hastur more out of interest than honest devotion. I thought a crazy person dressed in yellow would. Make an interesting Character.
But if you demand I follow the rules, then I will. But I think you should give Chaos a little slack.
Otherwise if all chaotic characters where loners you wouldn't have goblins, drow, several good societies, and the silver ravens would be a lost cause (chaotic good anyone?).
Honestly Chaos doesn't make a good leader, they do however make excellent followers, or leaders of revolts.
As for the Hastur, if he isn't an option I'll change over to Lamashtu, and save my crazy Hastur worshiper for some other game.