Well, there’s one corner to the right of where that first photo is. It’s not really accessible since the whole check out area sort of blocks access. I want something you can see from a distance.
Some images of people (robloxians) playing guitar/ukulele/etc would be nice. E.g. you could put an image of a bass player near the bass display.
That said, looking at real images of music shops, often the ‘decorations’ are the instruments themselves. It might look nice to just fill the walls with instruments.
An Idea I have for you would to maybe just plant one of those tree’s that you see in the first image. If it’s too small, maybe add a fountain right there.
I would highly suggest that you implement some windows into your nice Music Store.
For your comment, Add some more benches. Add 3D musical notes as like a statue or something. Fill your walls with instruments. Fill it to the top! They could be the same model, but the more on the wall, the better it will look. Have you though about adding guitars and drums? You could add those in the center of your music store. You should have stands and allow people to walk on those stands to try out the instrument!
As I see in a lot of places made in Roblox, the actual scale of the build is much bigger than the place would be in real life. This means you have to find more stuff to fill it up. Real life is usually way more crowded than Robloxian life seeing as IRL people won’t spend money to build/rent space that is empty.
As stated in the post above, filling the space with stuff you would find in an actual music store would help.
There should be lots of images online of the interior of music stores that can give you ideas.