Hardwired is always better if you can do it. I would do like so, since the NVR already has PoE ports:
If using a router with DHCP disabled (essentially a wireless switch or Access Point), make sure you plug into LAN ports 1-4 and not the internet or WAN port.
This is what I would do. However, you said your exiting router is out of ports. So not to add confusion, think of what I about say as a separate project not related to the shop. Buy an 8 port network switch (under $20) and plug that into any LAN port on you existing router.....you now have 12 ports you can plug any LAN device into....nothing technical to do as everything will figuring itself out. Now you can move on to the shop.
There are a lot of good suggestions on here like running the cameras on a isolated subnet etc but considering how you describe your tech skillset that would be challenging for now.
For now, buy an inexpensive router and connect it to the new switch via cat6 - LAN port to LAN port. With connectivity complete the tech part is next.
The tech part:
-new routers come with DHCP turned on, you must disable this FIRST
-configure new router as a wireless access point
Use Google if the router's instruction are lacking, or repost so we can assist.