Can one join as many or as few of these challenges as they want?

Because
[quote=@Terminal]
The task is meant to challenge you, present you with something you've never had to do before. Broaden your horizons.
[/quote]

I've already done that, kill off a main character or favourite character. I often have a main story and then several stand-alone side stories/alternate universe stories and people have died in such side stories. So my biggest problem isn't the task itself, but inspiration for a new story with one of my favourite characters in which that happens >_< I've been going over options, but nothing decent so far.