If you stay nearer 60 dB(A) for the general SPL goal, you'll likely be OK from an EHS (Environmental Health & Safety) standpoint if you can keep the speakers at least a foot away from your service workers. If I were doing it, I'd try to keep the levels and configuration in a zone where there's no need to warn/train workers about potential hearing damage. So that's probably under 80 dB(A) for workers in your case, unless there's some local/national limit that is more restrictive than the EU's.
Regarding background music, my AI friend says:
"Below 50 dB(A) is considered “quiet” and unlikely to interfere with conversation or concentration.
Above 70 dB(A) starts to mask speech and can cause listener fatigue over time.
65 dB(A) is often considered the upper limit for background music in workplaces if communication is important."
So it's probably more ideal if you can keep your workers below 70 dB(A) if you are going to have a constant volume level. If you're going to have "listening sessions" at higher levels where activity and conversation stops, having a spot for the workers to get back from the speakers and relax while also listening might be useful (or just let them exit during those).
I can see validity to two different approaches to your situation:
1) Background music is often handled by ceiling speakers. You could easily have 4 of those that keep the SPL levels pretty consistent for both workers and patrons. It's not fun, but it's effective. A coaxial design can help off-axis uniformity. Car speakers are cheap and easy, but there are also ones made for home audio that have minimalist paintable grilles, enclosures, etc.
2) Being an artist, the visuals are probably an important aspect to you, and if you like the Japanese style listening bars, horns and tubes may be a good fit (though tube designs can be fragile). On the speaker end of it, finding some old horn speakers that you like the looks of, but are in need of cosmetic work might be a good approach if you want to do something quickly. While old speakers with cult followings can be very expensive, some less popular ones are almost free. As long as the drivers/horns are in good condition, the rest is rebuildable pretty easily. As @Endycia suggested, equalization can be very helpful, especially if the horns you like the looks of are more aggressive sounding than you prefer. You can tame a lot of ills with a good equalizer.
If you want to build, but not design the acoustical end of things, using a known good design can also speed things up. A few of those:
https://josephcrowe.com/collections/speaker-plans?page=1
http://www.troelsgravesen.dk/The-Loudspeaker-III.htm
There are a lot of Econowave designs. Just do a google image search for that and see if you like any of those.
If you have a more specific aesthetic you're drawn to, actual budget constraints, etc., post some pictures of speakers you like and more details and someone might be able to suggest a DIY design that's similar.
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I still say build it in. Its basically a large car stereo. Truth is that every room reverberates, and car audio is all about using those small room reflections to your advantage. Make it good, then eq it great.
Take a look at the Lyngdorf LCR "sound bar." Its pretty massive but they have the interesting idea of sharing two woofs across the 3 channels. Really sparks the imagination 😁