As a domain is only an administration, I would use option 1.
If you run the domain controller without any server this instance is only for administration and there is no influence to the running applications.
The domain contains a server-group for each app.
You might use the same host controller to start one server for each application, there is a small risk that one server take all machine resources but that's on your requirements.
Also you can run a HC exclusive on one machine for one application to avoid that.