Just wondering if there are some obvious issues I should know with specific companies, or in general with modern CCTV installations?
Friends don't let friends use Swann, or anything off the shelf at Bunnings for that matter.
Most of the "affordable" consumer grade stuff comes from Chinese companies that are partially owned by the CCP (for whatever that's worth). Most have had one or more complete authentication bypass vulnerabilities in recent history and in general they comply with the "The S in IoT stands for Security" mantra. ie, there is none.
Keep the systems off the internet, and if they do insist on remote access do it via a vpn. Prevent the cameras or NVR getting outbound access. Avoid the "cloud" based solutions. Make sure the devices are recording 24/7 rather than on-motion because guaranteed they'll miss the event you actually need the footage from.
Most consumer grade NVRs have multiple PoE ports on the back for a point-to-point camera cable install, but aggregating at a cheap PoE switch can often be more convenient.
Don't cheap out on storage. Thumbsuck 1TB per month per camera.
Companies like Hikvision or Dahua are about as far toward the bottom of the barrel as I'd recommend you go, and in general a camera is going to be a couple of hundred bucks. Recorder double or triple that, plus drives.
You can go cheaper, but you get what you pay for.
A step up from that would be a PC running Milestone X-Protect (free up to 8 channels) or BlueIris (paid and up to 64 channels). Personally I think BlueIris is a toy, but it's a decent step up from Chinese NVRs.