I assume that your issue with the music is from your employees hearing the same songs in the same order. I doubt that the customers are the ones complaining.
There are a couple of ways to address this.
You can use streaming services to randomly play music (such as Amazon and so on). You will probably be limited in selections unless you pay.
There are some streams on Youtube which last many hours at a time, but they will be in a specific order every time you play them. Stream them directly from Youtube or download them with a browser addon like Easy Youtube Downloader.
There are devices (laptop, desktop, Raspberry Pi, etc) which will allow you to have MPs's or similar either on a disk or on an memory stick and will play the songs in a random order.
I played with a windows software program called MIXX which is free DJ software. You can tell it to play songs at random AND in your case, schedule promos or 'commercials' which will play inbetween the music. It would sound like a radio station, but with your branding. Those promos could be specials or perhaps just announce the WIFI password periodically. The devices mentioned above and this isde woudl take a bit of technology and perhaps a tech guy to refine it, but offer a number of solutions.
If you have individual songs and want them in a particular oredr the free Audacity will let you record audio or join audio files together.