Best Auth/Enroll option for this use-case?

by Isaac Savage.  

Greetings,

I have two main questions for this group:

1. Is it possible for Moodle to use 2 instances of the Authentication/Enrollment options? For example, I'd like to control the auth/enroll from two or more different sources using the same "Method." Is this possible with any of the default Methods?
   
   
2. Is there a document that goes over the pros/cons of the different options? For instance, why would I want to use "IMS enterprise" versus "External Database" for enrollment? Or "IMAP" versus "RADIUS" for Authentication? 

My goal is to create a "standard" that I use that will be easy to setup on the Moodle-side, for every instance that I interact with. I'm not really sure how to approach deciding which options are best. Do any of you have opinions on the best strategy? 

To clarify, my use-case is to utilize my database and easily control auth/enroll into various instances of Moodle that are manged by a 3rd party. My main priority is to make it easy for the 3rd party Moodle-admin to get their end set up. And, I'm hoping to find a solution that will work even if they're already using the same "method" with another source of data.

Thanks for the help!

Isaac