purvis
Name all servers differently.
If you want additional servers to resolve web requests etc, then give them appropriate main domain names eg mydomain2.com, mydomain3.com
If web etc resolution is not important or required they can have the same main domain name as your main sme server eg mydomain.com.
It really depends on your requirements, of which you have told us very little.
As your servers will appear to be in server only mode, then there will be a lot of control being handled by your main router/gateway eg port forwarding & proxy pass to different servers etc.