Came to recommend Synology; I’ve worked on small systems (4 cameras) and large (30+ cameras). For home use you can probably get away with their smallest NAS which includes free CCTV software (Surveillance Station) which itself includes 2 camera licenses. Adding more cameras beyond those will require a one-time license purchase. While this is not the cheapest route they are easy to setup, manage and use.
I use SimpleLogin emails but route them through DDG and works great