Hi @colinr, welcome to the Caddy community!
Yes!
Yes.
There’s almost nothing to it! Just leave your sites where they are and point Caddy back to them, exactly like you said. A basic proxy looks like:
yourwebsite.example.com {
proxy / 192.168.1.6
}
(Yes, that’s an entire valid Caddyfile with HTTPS!)
Here’s an older thread here on the forums with some discussion on reverse proxying Exchange, including some more examples: Exchange Server and Caddy
Sounds like an excellent setup. Go for it - and come back here if you run into any issues or have any other questions.