The tannins from wood do aid the fish, and while some wood takes forever (it seems) there is wood that is not as bad for continuing tannins. I use Malaysian Driftwood which is very dark brown; it is heavy so it sinks immediately without have to waterlog (unlike most other wood), and I have found it better regarding the tannins. I never see tinted water in my tanks now, and I have tons of this in my tanks, I will add some photos to illustrate. This is essential with South American fish.
Rock, again is not natural, but no harm in having some. You haven't mentioned parameters yet, but you will want the water soft and slightly acidic for these fish, and that means avoiding calcareous rock. The rock youwould use for your rift lake cichlids is no good here if it is calcareous. "River rock," being rounded pebbles of differing sizes, is usually safe; I have this in my SE Asian loach tank as it is natural to that habitat, but rock in my SA tanks is little or none. I buy my river rock from a landscape/garden outlet.
We will need to know the lighting specs and water parameters to say much about plants. But floating are important in these tanks to not only dim the light (which makes the fish more colourful and less stressed) but they also do a good job of using nutrients like ammonia/ammonium.
The first photo is my present Amazon riverscape, done in a 4-foot 70g tank as you are intending. The second is a 3-foot 40g Amazon flooded forest. Dwarf cichlids were work in either of these (forgetting the temperature issue for the moment).
Byron.