I would recommend making your own NAS instead of buying a Synology or something similar. Check out !selfhosted@lemmy.world. Hardware will cost a bit, but it's far more worth it.
An extremely good resource to begin learning the server environment would be https://esc.sh/projects/devops-from-scratch/. He has youtube videos that are really well done, I would strongly encourage you to watch atleast the first few videos as they cover topics that you will need to learn, such as : networking, explaining how linux works, etc.
After watching a couple of his guides and learning from them, I would recommend starting a basic server using an old computer or the likes that hosts a couple of apps you will be using. Nothing important like a password manager, file storage, etc, just yet; simply the basics so you get a better understanding of using linux as a server. My recommendations of stuff to try out:
- Installing PiHole using docker / docker-compose
- Installing Wordpress using docker / docker-compose
- Setting up a Wireguard server (there are also docker images, such as wg-easy) so you can connect to your home network from wherever, and use whatever services you are hosting (important if you wish to use your future NAS while not at home)
- Installing Nginx Proxy Manager and learning how to reverse proxy your services to a hostname
After that I would recommend you transition to Proxmox as your OS, learn from there, and then start hosting file managers/file storage (Network Attached Storage part), zoneminder/frigate for the camera system, etc. Patience is key with this type of learning.
For the hardware part it's all up to you: amt. of storage, amt. of ram, how big the chasis will be, power-efficiency, motherboard with features you want (ex. more pcie for 2.5gbps network card), cpu depending on how much processing power you need, ... You will need to do your research on this, but I recommend getting a NAS after you understand how docker and the works function, and to tailor to your needs.
If you have any questions let me know, hopefully you can understand what I was trying to say, not the best at conveying this type of information lol.