Here is the thing, reef systems are going to be complex and expensive and require a lot of work no matter what you do. In addition they require the reef keeper to be very knowlegable. In my opinion this makes them unsuitable for a place like a car dealerships. You need a system that looks great, is easy to maintain, is comparativly low cost, and can be run by anyone.
I think you'd be far better off setting up a conventional FW tank that is fairly large, and keep good size fish in it. That is, fish you can see from across the room. For the aquascape I'd use course aquarium gravel, the epoxy resin "driftwood", and plastic plants. If your into decorations, you could use the large ones for something like an underwater city. This way it's real easy to set up and maintain. The livestock can eat flakes or pellets, and if they get a disease, treat in the main tank. There is no expensive equipment required. You will not need a controller, or calcium reactor, or ATO, or sump. You will not need high end lighting or RO/DI water. A simple filter system will work just fine. Simple water changes and filter cleaning is all you will need to do for years.
Also, keep in mind that most people not involved in the aquarium hobby have no idea what they are looking at. To many, you will have a great looking tank simply because of it's size.