Actually, I’ve worked out a way to get let’s encrypt to get certs for multiple domains and not redirect to the primary domain. Multisite Configuration with Let's Encrypt and no reverse proxy
@AstonJ, would you be interested in testing my howto? I’m 90% sure that it works, but it was some weeks ago that I last tested and I’m not entirely sure that the instructions “work” for someone who’s not me.
If you want all the sites to have the same plugins and be upgraded all at the same time, multisite is great.