Read the WiKi at the top of the page. The Cliff Notes will help you a lot. A decent, relatively inexpensive, low light camera is the Dahua 2231R-ZS. Starvis sensor, 12x varifocal, single steam, no audio, but under $130USD from Andy at Empire Tech.
I can't answer regarding an NVR, don't own one and use Blue Iris. The 5231 series seems to provide an even better image than the 2231, but the 2231 is no slouch by any means. I don't know how much detail you're looking for or at what distances you're trying to work at. Generally, higher MP will provide better detail in well lit situations but will suffer in low light situations. If they're outdoors, I'd stick with 2MP until a, true, Starvis sensor becomes available in higher resolutions at a reasonable price, but I'm cheap and want good low light performance with all my cameras.