Hi Dave,
Saw a recent purchaser confirm he was able to get the Lorex LNB8005 to work with
Blue Iris. I am using a Dahua NVR, note a lot of people here really like Blue Iris.
Lorex, as a brand has carried numerous different types of products - some better some worse - the 6 4k camera kit you picked up is definitely Dahua OEM - which btw Qsee also uses for their 4K line of cameras. As such I believe this kit you picked up at Costco to be a very good deal, leaving you 2 more ports which you can custom select additional cameras.
I calculated that at 25ft with these 4K cameras you will have 100ppf - the spec for ID distance - of course this is during good lighting conditions, and thus positioned correctly you should be able to have enough pixels on target at 30ft to read license plates in the images. ( license plates need less pixels per foot vs facial ID )
I don't know the FOV of your 3MP cameras, if the FOV is similar to the 4K cameras in this kit ( 88 degrees ) you should see a significant jump in the ID distance. ( est for 3MP 88 degrees horizontal FOV = 15 feet for the ID distance at 100ppf - thus the 4K cameras gives you 10 more feet to get a potential ID - fairly significant imho for such a wide angle camera ) Of course if you need to extend your ID distance further you can get a varifocal and reduce the FOV.
If the other cameras are also POE you should be able to reuse the wiring and just unmount the old cameras and install the new ones.
If you have a darker spot around your house you can pick up 1-2 Dahua starlights to cover those and in the end have a fairly nice system imho.
Have Fun setting it up, and remember you can bench test the Lorex kit before unmounting your older cameras so you can see which you like better.