Congratulations on your anniversary. Be glad it did not coincide with the NFL draft that drew 600,000 people. The rest of the the town is empty right now.
Nashville has grown at a crazy pace the last 4 years, it is nuts. I have lived 23 years here and it is crazy to see this once small city to grow like that.
You do not mention what dates you are coming down but...(oops I see you said May)
Downtown is mandatory, Honky Tonks, the earlier in the day the better to avoid the crazy crowds. Beer tastes good during the day too.
Hot Chicken is a must, even if you get the mild, Pepperfire, Hattie B's, Prince's.
Guitar shops, unless you are wanting to look at some high end stuff, I'd skip it. You have GCs in your town.
The area by Third Man Records Studio/Store (Jack White) not far from downtown has some breweries nearby. Look up the area to see if you are interested.
East Nashville, a very short Uber ride and you are in Hipster/Artist/Musician and Gentrifiers live there. There are a few cool bars and restaurants. For Pizza go to 5 Points Pizza.
Vanderbilt Area or "West End" there are a few cool bars, Chuy's Mexican Restaurant is a chain but it's cool and probably you do not have one on your neck of the woods.
Centennial Park for a daytime walk, and look at the Parthenon. Classic stuff. Also on the West End.
The Opry House is on the East-ish Side, not proper East Nashville but only the Opry Mills Mall is nearby and a bunch of cheesy country shops. Id' skip it.
If you happen to be here on June 8th The Rock N' Roll Residency is playing a show and that would be a must. They are bringing the guys from That Metal Show for comedic entertainment. (Not Eddie but the other two)