@newbury
IMO you are exactly on the right path by hardwiring as many fixed network devices / station; basically if there is going a fixed network device... wire it. Of course the PoE cameras will be wired but depending on what you are using for an NVR & where it is going to be located you may have to plan your wiring appropriately.
Ethernet connected (hardwired) devices will have more consistent speeds & lower latency (as long as the wiring & terminations are done properly) then 99% of Wi-Fi networked devices, even with the release of Wi-Fi 6 Routers, & this has nothing to due with your metal buildings but a very good reason to hardwire... Also wired networks are usually more secure if setup properly & of course the benefit of PoE.
As mentioned prior you will only want solid conductor Cat6 for your cable runs.
All Patch cables used should be Stranded Cable.
Cable runs should be tested - especially is using PoE equipment
For termination of connectors we prefer the 568-B wiring over 568-A
You can purchase cable at any of the big box stores (HD - Lowes) but if you have a electrical wholesaler close by I would try them. Just make sure you are purchasing a quality cable & with the same specs when comparing pricing, standard Cat6 is usually 550MHz which will handle way more bandwidth then you will need, so don't let someone to talk you into Cat6a at twice the price.
Wish I could give you an online supplier but we are in the industry & purchase wholesale so most of them will not sell to individuals... if you have any questions on wiring / between building connections / product PM me & I will see if I can help...