Thinking of changing focus to rift lake

I have a 45 gallon hex tank that was currently planted. I wasn't giving the plants the attention they needed, they are looking pretty pathetic. I sold off my pressurized CO2 a month ago becuase I thought I'd get rid of the tank. They I decided I didn't want to. I need to change the tank to another set up.

I have always wanted to do a rift lake set up. I don't have the perfect tank for it, but I think I want to try anyways. I am leaning towards Lake Malawi, and I think I want to do mostly zebras.

There is so much info out there that I'm pretty much confused. Could anyone point me in the right direction. I'd also like to do something very cool when it comes to hiding places. I was thinking of something cylindrical in the middle of the tank, not sure how feasible that is since it will cut down swimming space (they can still go around it). Any ideas are appreciated, I was going to go with straight lava rocks. My water is already very hard and of a high ph: 7.8 naturally. I've never treated, and I have some tetras that are 3 years old.

I know that, but I'm not going to buy a new tank. How many mbuna could I safely house in my tank? What if I had something like a rock wall on the back with plenty of hiding spaces?

The tank is 23 inches wide, and about 40 inches high

I don't know anything about shell dwellers. What I want to do is build a fake rock wall, using sheets of styrofoam which I would seal and paint to look like slate. I know I dont' have floor space for hiding places, but why would vertically stacked rocks not work? Wouldn't that be even more like their native habitat to begin with?