You write that you need help. From the questions it sound like you need experience. You may not like my answer.

BTRFS and ZFS are very similar, try them out figuring out.

Try LXC if it doesn’t work for you, use standard VM.

There is nothing wrong with have all in one machine, one VM per service or a hybrid.

There is nothing wrong with using a WLAN as long as you accept the consequences of that.

I think you should try it out and get some experience, what is the worse that can happen? You learn something and try something different.

It reminded me of Pacific Drive

Then a tool like netdata may be the thing.

A tool like Librenms will give you this.

Do you want to use desktop app or systemd timer?

How can I be sure that my traffic is routing to the Wireguard VPN?

Use ‘tracepath’.