For a 30 I would recommend:
Lot of rockwork and a pair of julidochromis
Light layer of sand covered in shells for a colony of shell dwellers (Neolamp. multi. are my favorite)
Mxing the two can work in this size tank, however, I find that even in my 55, which is a whole foot longer, that there are still face offs. And with the ease of breeding, you can quickly overpopulate a tank before you know what to do. I personally would choose one or the other.
Breeding for both is VERY easy.