Can I stock certain fish?

[taintedpolarity]

I'd go with all mbuna, Lake Malawi is pretty big with lots of different tempered fish. Plus mbuna look good IMO. If you wanted the shubunkin that could work for a while, but you'd definitely need to build a pond, especially since you probably won't want to keep just one fish and do all the maintenance on the tank/pond. With the mbuna, you wouldn't need to upgrade the tank.

 

[Fat Homer]

^ Not to mention Gold fish tend to prefer cold water, where as most if not all cichlids prefer more tropical temps so that combo wouldn't work...