OpenWrt is perfectly capable of doing what you want. Just turn the device on... voila you have an access point + DHCP server + ipv6 router advertisements, and everyone can connect to the network and get ipv4 and ipv6 ULA addresses...
The only question is whether it will be reliable and low latency enough. As I said, disabling some of the lower data rates will help. I'm not sure there's a GUI method for that.
Cool. Then it comes to hardware choices. I haven't found a "bird's overview" over what different types of devices can be used with OpenWrt. Like, I learned today that the Raspberry Pi 4 has "junk WiFi", but why is the wifi junk; how can I know what devices are good and bad, and get good value for my money? The question "what" devices will work with OpenWrt is available on openwrt.org, but I can't find any in depth articles of "why".
Yes, I agree it's a bit overwhelming, part of it is just that the field is SOO large. The RPi wifi is junk because it's a tiny built-in antenna only and an under-powered wifi chipset.
Gl-inet stays very close to OpenWrt standard distribution, which I think means they optimize their choice of hardware to work well with openwrt. So I can recommend you start there. Mostly when it comes to wifi quality there are three things:
If I were undergoing this project, I would probably start here: https://www.amazon.com/GL-iNet-GL-AR750S-Ext-pre-Installed-Cloudflare-Included/dp/B07GBXMBQF
also, unless you really care about secrecy of your music, you might try disabling security on the wifi, then none of the devices have to do any encryption at all. (BUT: caveat... only log into the router via a wired cable, or a second secure SSID so no one can sniff your router root password over the wireless)