I have one server over the Internet, on virtual, rented VPS. I have multiple PCs over the country. I'll use VPN probably anyway. But what if not? Is transmission between agent and server secure enough ?
I'd recommend looking into using LsAgent: https://www.lansweeper.com/knowledgebase/lsagent/
With LsAgent you can scan devices that aren't in the same secure network as your server, via a relay server. This would be far more secure than exposing the listen port of your Lansweeper server to the internet, which you'd need to do if you wanted to set up a direct to server agent scan over the internet.