Help with new setup

[Dr. Lars Hanke]

I'm using Cyrus-Imap for about a decade and it just works - so much that 
I lost most of the administration knowledge I once had. ;)

However, the new setup should be different in a couple of ways, and I'm 
asking for best practices, howtos, and other write-ups that I should 
consider to achieve the following goals:

1) Users shall authenticate to Samba4 AD, ideally use Kerberos.
2) I did Kerberos authentication in the original setup already, just to 
find out that virtually no client (most systems run Linux) supported it. 
Has this improved?
3) Users, i.e. AD entities, should be able to manage several distinct 
mail accounts, like a private and work account.
4) Functional mailboxes, which do not exactly belong to any user, but 
must be accessible by multiple users.
5) Sieve support using the same authentication.

Thanks for any reading pointers,
  - lars.