Keep playing with it till it feels right. When it comes down to it, the tanks should appeal to you. If you like it great. I'm new to this also but have learned alot in the last 6 months.
It's a small tank, so it will be challenging. I say create a focus point instead of having rocks strewn about. And don't feel tied to the rule about having odd-numbered groupings of rocks. It's perfectly fine to use 2, or 4.

