Imapsync. Used by Linux engineers since forever to copy email accounts from one server to another

If you do self host dns make sure you have at least 2 vm’s on different subnets (not the same ip ranges) and if you really go smart about it have them hosted in separate cloud providers to mitigate the risk a bit. Then make sure you are aware of how hackers use dns servers for example dns amplification attacks with dns to prevent yours from being used. There is documentation and CIS guides on this. But overall it is not scary. Just a bit of initial admin to get going. As other have mention there is bind, powerdns and that other one that was mentioned Technitium or something (never heard of it before). But as others have mentioned before, Cloudfare really is a good option to selfhost without the infrastructure requirements.

As with everything in life you need to crawl before you run. And as someone mentioned before skills issue. You can assume most people who self host are Linux engineers / Devops engineers. So they do these kind of setups daily. This is why these channels exist. So we can assist or guide. So you can learn as well.

That is what rook-ceph or longhorn is for. Longhorn is good for beginners

Minio self hosted. Just get a server with loads of storage. This will work most cases. Unless you intend to host an app that is going to be used world wide / needs location based cdn, load balanced etc. Then a commercial service is a better option