Yep, agree with lowering the heater and horizontal so it’s easier to hide and for temperature diffusion in water column.
More plants definitely, get easy to care for plants like vallisernias, cyrptocorynes, elodea (anarcharis) you can also add anubias and maybe java moss as well by glueing or tying them to some of the rocks.
Sharp rocks can damage some fish specie bodies so do be aware of this.
You can make caves and focal points with some of these rocks but ensure it’s secure and won’t fall and trap some of your livestock.
Hard to tell from your pic but does not look there there is any background on the rear glass, putting plain blue or black background on the rear glass will help to showcase the rocks, plants and livestock as that usually helps the colours to pop a bit more.