Regarding integration with a PHP site and having a single login, you may want to read up on this too:
https://meta.discourse.org/t/single-sign-on-help-class-for-php/13104
As for your larger business goals, not sure without digging deeper into what you’re trying to accomplish, but it’s probably worth exploring the forum here, searching around for similar ideas to see what people have been able to do with it.