Here are a few more discourse links to consider.
Multiple sites in one Trellis, like you already considered.
Sounds like you want one Trellis, but each site on a separate server in production (adjust hosts/production as in “option 3” at link). If/when you want to limit server.yml to run on a given site/server, you can add the --limit site-1 option to your ansible-playbook command.