Sure, setting up a "gold" template is a great way to do it – I assume you created a template from the default settings, and just changed the few items that should be different (such as limits and quotas and the like).
Whenever you go to add your first account, you’d go into Create Virtual Server, and as you’re setting up the account details, you would set “Server configuration template” to your “Gold” template.
Then, once that user logs in, if they add a new domain to their account, it would indeed become a sub-server.
And yes, they would need Virtualmin access to create a sub-server – but when you create their account and domain, part of what Virtualmin does is setup a Virtualmin user giving them a limited set of permissions, including the ability to add those 50 domains.
actually the best thing to do imo is to clone the default template and experiment with the options. create a server and log in as that user to see what you can do and what permissions you have when in doubt.
thats the best way to get to know your product and limits.
Personally I wouldn’t set things to automatic as you then do not know exactly what the limits are.
I believe the "For Use By" is going to effect when the template presents itself as an option.
In your case, I’d probably make it available for top level Virtual Servers.
That means the users you create can be given that template, and will be assigned the privileges given to them within that template.
Whenever they create a new Virtual Host, it’ll default to using “Default Template for Sub-Servers” – which is fine and what you want, they can only make as many of those as they have permission to create – as set when you created their account using the Pro Plus template.
And I will set the default template to the most used one to make it easier for me. I assume that it wont like more than one template being set to the default. ( But maybe its clever enough to reset the others to "no" when you set one of the templates to "yes" ? )