The idea with Ethernet is you shouldn't have lots of intermediate connections in the cabling. Couplers introduce both signal and ampacity losses as well as opportunities for moisture to enter. Unless you use a POE switch, each cable should ideally be a home run from the camera to the NVR.Sounds like for my internal wall and attic runs, Ethernet cable should be just fine.
Make sure you use Ethernet cable that has the fattest gauge (lowest number) solid wire (as opposed to stranded) you can reasonably get. CAT6A is typically 22ga. CAT5 is typically 24ga.