If this is possible, it is better to have 1 DB for the master that is a private website and not public.
After that, create you slave site that can be domain, subdomain or subdirectories.
In the following, I will suppose that you are using cPanel as you written directory /public_html/slave1
When this is possible, never put your "addOn domain" in the root of the "/public_html" but prefered another root directory like "/domains". This avoid to have your addon domain also present as subdirectory of your primary domain.
See the technical document video 0.b slide 21-24 for the recommended architecture.
www.jms2win.com/en/tutorial#jms12x-0b
Put something like /domains/slave1.com/public_html
Concerning the DB, if you are allowed to have unlimited DBs and also allowed to share tables between different DBs, then it is perhaps better to have one DB per website.
If you just have very few website < 25 then perhaps it would be easier to share the same DB for several websites.
See also the list of extension that can be shared.
Becarefull that most of the extension also require to share the users.
www.jms2win.com/en/list-of-extensions?vi...id=269&Itemid=53