Yes, you set the client to the IP or host name of your server. The server’s IP has to be reachable from the internet.

https://github.com/techahold/rustdeskinstall Or if you are using Proxmox VE https://community-scripts.org/scripts/rustdeskserver

Yes it will be fine. Much will depend on what OS you will run and in turn how you want to do storage. NAS drives might not be necessary if you going to use software defined storage. If in your budget consider a CPU with more cores for virtualization and docker.

Overall nothing wrong with that configuration. But if you really get into all the awesome stuff you can self host your two constraints are RAM and CPU cores.