Your scape only matters for about a year. Then the corals take over. If you can plan for a year from now, you can create an awesome scape. This is my old 65. Just try to make it sturdy and give the fish lots of places to sleep.
Negative space is awesome and super fun to build. If you go that route, I suggest using thin super glue from gluemasters and rock powder. It makes bonds harder than the rock instantly and you won’t need to mess with mortar and the joints already blend since it’s powder from the rock.