Lost - Multi-site, openid, same database, LDAP - what to choose?

Hi, I'm lost.

I work with a non-profit buddhist group. We want to manage access to 4 Drupal websites, a Zimbra email server, and other web apps (Google Apps, possibly Zoho or Allegro). I'm trying to figure out how to do this for a group of 200 people without creating a permanent full-time unpaid position for myself. A solution that was simple enough to hand over to a non-techie is my only hope :-)

There seem to be alot of options. Has anyone tried and like a particular one?

I'd like to be able to:
- manage users access to content with some kind of donation memberships - I'm planning on using Ubercart and Authorize.net's ARB.
- integrate with a Zimbra server (Zimbra has an LDAP server).
- integrate with other web apps we haven't decided on yet (We currently use Google Apps, but are looking at Zoho and Alegra)
- manage access permissions by:
- centrally including users in groups
- managing a groups access permissions centrally if it's easy, or in individual applications if it's harder.

How would you do it?

Mike

I saw these options:

Hard-core Database based options:
- "Multi-Site, Single Codebase, Shared Database, Shared Sign-on 5.x" here: http://drupal.org/node/147828

Multi-site Type options:
- "Domain Access" + "Shared Signon": http://drupalmodules.com/module/domain-access + http://drupalmodules.com/module/single-sign-on
- The Multi-site modules: http://drupalmodules.com/module/multisite-api

LDAP:
- LDAP - http://drupalmodules.com/module/ldap-integration

OpenID type options:
- openid module (poor reviews on drupalmodules.com) - http://drupalmodules.com/module/openid
- openidurl module (don't really understand it) - http://drupalmodules.com/module/openid-url
- cas module (legacy?) - http://drupalmodules.com/module/cas
- singlesignon (legacy?)