For NVR, I'd recommend going for 16 channel one. It's a much higher price, but it's also a one time purchase. And it's mostly a 1k price increase compared to 8 channel ones.
You'll have to buy PoE switch separately anyway, so you can cheap out there.
Here's a 4 channel NVR
Here's a 16 channel NVR:
The one above has space for only 1 hard disk, while some others have 2 hard disks, but also cost more.
I'd recommend going for TP-Link switches if you have any other PoE appliance than the cameras on it. Otherwise, CP Plus switches work as well.
Again, the 4 port one costs 1.4k, so for 500 more, you get a lot of future headroom. And you can chain the switches later on as well.
As for cameras... well, if you want color at night, there's the TruColor or whatever Hiksvision calls it. Otherwise, go for 2MP cameras if you're going the 4 channel route, or 5MP ones if you're going the 16 channel route.
You can go 2MP for any NVR, but higher resolution also means higher quality video recordings. Still looks kinda shit compared to what you might be used on a smartphone for example. But it has its upsides.
Higher resolution also comes with higher storage usage. With 4 cameras at 5MP each, and a 2TB HDD, you can record for 1 to 1.5 months I think. Could be wrong.
These are just suggestions. Please do your own research before buying.