Yes, definitely try it. I'm a big believer in enriched environments: plenty of hiding spaces, plants, rocks/driftwood, and sandy substrate. Makes it more secure,enjoying, and entertaining for the fish imo. My del loves to torpedo into the sand and bury herself. My other polys love being under the driftwood. Since I added more plants a few days ago, they have been more active exploring the tank.
If you are wanting to go a more minimalist route: sand, maybe a driftwood piece, a few stones, and a plant or two? Good luck with whatever you decide to add!
I'd say you are fine. Like mentioned watch nitrates they can climb quickly. As for UJs and agression you shouldn't have to much trouble you'll get the trouble maker everyonce in a while but they usually get over it once someone puts them in their place.
Id probably stick with this and not add much. Only because of maintenance/nitrates i Like like to understock.
Maybe 1 more upperjaw.
I get what you mean about decor. I always had iasues with polys and territories. I just however added a few pieces of dw to my tank because i have a pretty good feel for the personalities (pretty laid back)