Is there any art you particularly love? If it were my room, I would hang a single, large-ish piece of art over the server, remove the shelf toward the right corner, and then select something for the top of the server. Seems like anything you hang on the wall over the server is going to crowd that little shelf. As for what goes on it, maybe a glass hurricane, or one or two serving pieces to display.

Whatever you decorate that server with should be simple and easily removable if you actually use it as a server. I would probably just use a vase or an interesting serving piece - maybe candle holders (with candles) that I use frequently at the table. As for the wall, art. Something you like.

Minimize whatever you put on top, as Marymd7 says. One vase, a pair of candle holders. Period. That's it. And art is personal, I'd go with something a little narrower than the server itself.

The server is going to look weird because that shelf to the right of it (our right looking at the photo) is going to make the blank wall over the server look unbalanced. I would move the shelf over the server. Or get some large art to hang over the server at eye level with the shelf to balance it.

I agree to leave it mostly plain. Mine are crammed full of tea sets on one side and wine and bar stuff on the other (I have two). My long term plan for mine is to put shelving for display above and declutter. I don't have to use mine for serving though, I have a pass through counter from the kitchen.