Will it be a good practice or a maintainable solution to install multiple SSL sites on a single SP farm (web app per SSL site) or should I prefer virtualized Is it really gonna work fine without problems and is maintainable (I could also alternatively separate the SSL web apps each to its own virtual SP environment)?
A single SP farm vs virtualizing many SP farms?
A single SP farm can handle multiple SSL sites, as long as they're on unique IPs. A separate farm per site would be a waste of resources. SharePoint is designed to handle multiple.
As far as maintainable, that would depend on your site collections and content databases and anticipate database sizes. Also, the more web apps you add, potentially the more RAM you'll consume.