Throw in a Dell Sonic Wall, and make the POS company happy. They're the industry standard for a reason, where I wouldn't use a consumer based product for this instance, due to the security issues with many of them. They want a SECURE firewall in front of those terminals, and it keeps you in compliance with the latest rules.
Reading what you have, your current system is not in compliance, with the debit machines accessing the internet with NO FIREWALL. The fines are not cheap, if something happens.
The latest trend is Ubiquiti, as you can easily remote manage it from an app. Many other companies have followed suit. I've used the Snap AV products for years, as they have their OVRC app to manage all this, as well as a wattbox for remote rebooting, incase I loose internet, or just a fresh reboot weekly.
It sounds like your cabling is fine for what you use. The latest trend in wireless, is Wifi 6, and just use POE switches for access points to get your wireless needs. This also frees up resources for a router, to just be a router, instead of going the all in one route. Also, this future proofs your setup, as with the changing wifi standards, you just program new access points as needed, instead of having to rebuild your entire network again. D-Link makes some solid access points, for reasonable, as well as their managed 1200 series switches have been bulletproof for me. Ubiquiti has APs, as well as managed switches, again, if you wish to switch to their eco system.