Personally, I would separate one of the structures to give a bit if separation and create 2 separate structures.
Also, depending on what type of fish you plan to keep, I would probably epoxy some, if not all of the shelf pieces so they have a slight lean forward. This will create an overhang effect that a lot of reef fish need to feel safe which will actually cause them to be out and about more. It also gives you some more flexibility with coral placement because you'll have an incline toward the back vs. a flat surface, will make for a better front on look.