Zimbra, Virtualmin, LDAP, and Linode

Heres my plan:

I am starting a Web Design and Hosting company. I have decided to use Virtualmin & Zimbra for Hosting CP's and Mail servers, respectively. Now, I have 3 VPS's right now (Linode) but I can purhase more, if need be.

My basic idea is to do the following:

Have one VPS set up with Virtualmin as main1.mydomain.com (With an A record pointing to the correct server from the main1 subdomain)

Have another vOS setup exactly the same as the first, only called main2.

Both of these VPS's (main1 & main2) will use LDAP, so that users can login at either URL and still get theyre account settings, as well as so that the Zimbra mail server can retrieve mail settings.

Have the third VPS setup with Zimbra mail server, and configure it for multi-domain support and logins (so users would login with user@fulldomain.com and they're password) to get there email.

Now, onto the questions:

Can I do this?

Is it possible so that any user can go to mail.customerdomain.com and be forwarded to the mail server?

Can I re-direct mail from the virtualmin servers to the zimbra server?

Can a user go to mail.mydomain.com and be forwarded to the zimbra server?

Can I use LDAP to accomplish some/all of these tasks?

Thanks a million,

Adam Del Vecchio