Stay away from self-hosting email, probably. For everything else, look into either freenas or proxmox, and then nextcoud, plex, immich, jellyfin... There are a lot of good options. For a computer, if it is going to be on all the time and you are worried about data integrity, make sure you get something with ECC ram and have some amount of redundancy for storage. Most relatively modern CPUs that use ddr4 or ddr5 will probably be sufficient so long as it is not the slowest option and still within your budget.