I'm assuming you're on Debian or Ubuntu. You can set up automatic security updates on Apt, and if you have a firewall you're halfway there. Then I would make su

I'm assuming you're on Debian or Ubuntu. You can set up automatic security updates on Apt, and if you have a firewall you're halfway there. Then I would make sure each website has its own user, group, and www-user and using file permissions, make it so each virtualhost doesn't have access to others' files. If you wanna be extra safe you can have each site on its own vps. Although what's nice about keeping a bunch on 1 big vps is that you get to save a lot of time managing it as it can take a while to propagate changes across many VPS and if they all have different setups it can get confusing. To do 1 site per vps properly, you should have fleet management going like Ansible or Puppet so that you can maintain them all easily. That way all the code is hosted on a build server, and individual environments get built for each site.