Here's my predictions/suggestions for the Ambassador (and it's KDF counterpart);

Most assume that the KDF will get the K'Vort, which is basically a Cruiser-sized Bird of Prey, but without the folding wings. To that end, i'd suggest the following BOff layouts;

If equal for both factions:
Commander Engineer
Lt Commander Universal
Lt Tactical
Lt Science
Ensign Engineer

If tailored for Federation:
Commander Engineer
Lt Commander Science
Lt Tactical
Lt Science
Ensign Engineer

If tailored for KDF:
Commander Engineer
Lt Commander Tactical
Lt Tactical
Lt Science
Ensign Engineer

I have no canon suggestion for what these ships might have for unique abilities. And obviously due to their role, their individual stats would be different (K'Vort with more maneuvrability/firepower, Ambassador with more shields/support).