That tank just cries out for a large group of...something :-) First thing I thought of was Terribilis.
I do love terribs, but I already have a group of tincs coming for this setup. I am thinking of finding someone who wants to build like a 250gal long tank for gold or mint terribillis. If I did that setup it would be all understory growth and larger plants like monstera and ferns. huge open areas of mossy ground space and dark gloomy wood. I great contrast to the yellow or mint green frogs.