You can use any Synology NAS. Which one you choose depends on how many cameras you’re using, and what frame rate/resolution they record at. I’m using a DS115J ($100 plus the cost of drives if you don’t have any lying around) because I only need a couple of cameras.
Synology has a calculator for this. https://www.synology.com/en-us/support/nvr_selector
And while it’s true that a Synology NAS isn’t a dedicated NVR, the software that handles cameras is the same software that Synology uses on their dedicated NVR boxes: https://www.synology.com/en-us/surveillance/7.2
There’s a great community integration that lets you use Surveillance Station cameras as motion detectors (and lots of other stuff too). Synology Diskstation & Cameras
For offsite cloud backup, I am considering Backblaze B2. They offer a Synology app, 10GB free storage and up to 5000 free upload/downloads per day. That’s plenty for me since I will keep using the Synology app/web login for viewing of my files. I’ll only use the offsite storage if my NAS were to be stolen in a breakin.
https://www.backblaze.com/b2/cloud-storage-pricing.html
I will report back when I give it a try. I already use Backblaze for my offsite backup of all my other devices and they have been flawless. (on a side note, if anyone is interested in Backblaze, here’s my referral link: https://secure.backblaze.com/r/005s98)
There are also Dropbox and other apps for Synology NAS. You can pick your favorite.