Nice looking "tree" for just a years work.I'd try to thin it out some more so that the individual trunks are more visible.But, and it's a big but....without seeing the tree in person and being able to look at all sides...it is awfully difficult to give styling advice on a clump style.Can you use wedges to spread the trunks further apart form each other?How well fo they sprout from pruning?Obviosly with nandina you don't expect ramification,I presume.You may have to wire individual leaves to get a more layered look(if that's what you are after).
~LOL~...I guess that was more questions than answers.
andy