I bought a system very similar to the one you describe, but directly from Lorex about 2 years ago. Four 2MP cameras, 8-channel NVR. I think Lorex equipment is re-branded DaHua, so quality is decent. When I bought mine, customer service and tech support were good. Then they outsourced and they turned to . . . uh . . . I'll just say worse than useless. They are recovering, but CS is still bad. You have to be able to understand heavy Indian/Pakistani accents and tolerate the insufferable scripted responses. Tech support is decent again. I will have to say this about their support. Lorex definitely DOES stand behind their products. I ran into a problem with the NVR and it was replaced with no arguments even though it was just days from going off warranty (2 years). Tech support did login into it and tried a few things, but had no luck diagnosing the issue. They are also replacing two of the 4MP cameras that started acting weird, and they might even have been just past warranty.
If you buy a Lorex system, they try to lock you into Lorex equipment and Lorex prices forever. That is not all bad since you do get support with them, and that support costs money. The cameras, and I presume the NVR as well, have proprietary firmware, and in the two years I have had my equipment there have not been any firmware updates to either the NVR or any of the cameras. They have a reasonable selection of devices, but somewhat limited. For example, there is no lens selection. They only have the cameras that give you the widest field of view. If you want a camera that has a narrower FOV to focus in on a particular area, too bad. You CAN use other ONVIF compliant devices with the NVR, but some configuration options are not available to the NVR. I have replaced one of my Lorex cameras with a DaHua that has zoom capabilities, and it is working just fine. More on that later.
Now for part two of the story. Like you, I was sure that 8-channels would take care of all my needs for the rest of my life. No doubt at all. Then I bought a 4-pack of 3MP cameras and all 8-channels are utilized. It's at this point in the story that I discovered this forum and Ali Express, and I now have 11 cameras, and I am thinking about a couple more (some as replacements for existing cameras). The DaHua StarLight cameras seem just too interesting to pass up, and I want a camera or two with either zoom, or PTZ capabilities. Since my NVR was full, that led me also to Smart PSS, and Zoneminder, both free.
Zoneminder, to me, is just too much hassle and there were a lot of things I didn't like about it. About the only good thing was that it ran on Linux. A LOT of stuff has to be manually configured, and that includes Lorex cameras, and I never could get the views the way I wanted. But I was able to get one of the 3MP cameras working with Zoneminder.
Since it seems like all recording software tor PCs is Windows based, I built a Windows machine and put SmartPSS on it T(that wasn't the only reason I built it). Smart PSS seems to work well, but I have an issue with it where it just stops launching after a week or two making me uninstall/reinstall it. I asked on this forum about that, and I seem to be the only person on the planet having this problem. You might have to change the camera protocol from "Private" to "ONVIF" but that is easy and quick, but after that it is fine.
You asked about ONVIF compliance, and one of the 3MP Lorex cameras I bought is definitely compliant as I am using it to test a new DaHua NVR, and the Lorex NVR will support ONVIF cameras as I have two DaHua brand cameras attached to it. I put one Lorex camera on my LAN, and SmartPSS had no problem with it as a ONVIF device. If I remember correctly, I seem to remember that the LOREX website even mentioned ONVIF compliance in the product description for that camera but I could be mistaken about that.
I have recently purchased a DaHua NVR5216-16P-4KS2 NVR and I am currently testing with it. The Lorex camera that I have tested does work as an ONVIF camera, but that leads to other issues. I do not know if this is specific to the DaHua NVR or restrictions resulting from running them as ONVIF devices, but configuring the cameras can be a problem. Sometimes, some of the configuration options are not available except from the camera itself. Modern IP cameras will have a "mini web server" built into them (sometimes referred to as the WEB SERVICE). Using a Windows computer (I don't know about Mac), you can use MSIE with a plug-in to access the camera itself. That way, all camera settings are at your disposal. If you have an NVR that has PoE ports and the camera is connected to one of these ports, you MIGHT be able to access the camera directly if your computer is also connected to one of the NVR's PoE ports. If your cameras are on your LAN, then MSIE with a plug-in should work. The latter is what I had to do to configure one of my DaHua cameras attached to my Lorex NVR. After the configuration though, it works fine.
I'm going to stop now. Sorry if this seems to ramble, but I was adding information as it came to me.
Wayne