How many applications are we talking?

If you don't need runtime, any good brand Line-Interactive UPS will be fine.

I've terminated them to my patch panel and plugged them into my switch, plugged the NVR into the switch and they talk over that.

you could probably fit 4 in a 4RU case if you just got some really long standoffs between the 2 motherboards. Then just need to dremel out the back of the case and you're set.

It's pretty easy to set up when it's dockerised, but when it's dockerised, it's much more annoying to get the plugins installed / working

They're not cheap everywhere unfortunately. I wish they were cheap for me!

Graylog is pretty simple

Install, point syslog to graylog, voila

Cisco 3750X with the 10G NIM is also an option if you only need 2 uplinks. It's getting a bit dated though, but can be had for cheap.

pfSense virtual router connect to a FTTP NTD and a Huawei LTE 4G router

Last time I did this, i mapped out which plug corresponded to which device that linux saw then wrote a script that told me which hard drive was plugged into where and put it into a csv file.

This was for my disk testing tower, so when it told me "sdb" had finished badblocks, i would know which hdd sdb was.

Brought the camera back to homelab A, double checked IP address, still on the correct range.

Put a device onto same subnet, can ping it.

Going to try and set it back to DHCP and take it back to Homelab B and see what happens again.

Brilliant, i was looking for something like this as well for a project, thanks!