Wow Kimichan, those are pretty some pretty stern words from someone who hasn't ever kept anything alive before. I hope you don't have to learn the same lessons I learned.
As far as fish go, I think that it might be cool to keep a jawfish, or a pair of jawfish (as our young friend pointed out, I am big on pairs). Most nanos are going to use LR for most of their filtration rather than a DSB. Thus, the disturbance to the sand from these cool little fish would be pretty harmless. Also, they tend to stay close to their burrows, and thus don't need a lot of swimming space.
Mike