Linux as backup machine, security concerns

Hi, i hope i'm posting this in the appropriate subforum.

First off i'll admit i'm not very familiar with how these things work, otherwise i wouldn't be asking this (probably stupid) question.

I have Linux Mint running on a laptop. I'm thinking about using the laptop as a backup solution for all the other machines in my LAN using rsync and/or FTP, and i'm concerned about the security of my data.

The laptop is online 24/7, connected through a VPN (OpenVPN client). The laptop also has a SSH server for rsync, and vsftpd for FTP. It has ufw installed with strict rules to allow traffic only to/from the VPN server, and the specific IP addresses of the other computers in my LAN. I also have a hardware router with no ports open in its firewall, since it isn't necessary for these services to function. The computers in question are all cable-connected, although wireless is enabled for one tablet device. Encrypted, of course.

Does this setup open any realistic threats for my data from outside access? I don't know why, but that constant connection to my VPN provider makes me feel like there's a door open somewhere, somehow, for anyone to walk through. I suppose there basically is, but can this be used to infiltrate the laptop?