
why do you want to restart everything from scratch

Furthermore, rebooting was not mandatory

I suggest we do not discuss content of resolv.conf or any other file but focus on Zentyal configuration from GUI. Do not take it the wrong way but for the time being, given debate we have, I don't think you have yet reach the stage where we can look at config detail from CLI.
Zentyal as DNS client:this is configured in network section ! be sure to add here some external DNS otherwise you will never resolve any external name
Zenyal as DNS server: do not change anything now that DNS is dynamic. Ensure DNS acts as cache.
DHCP server:you can (should) push Zentyal as DNS server for clients.
adding external DNS is useless (again)
No you don't need to install Samba to have DNS working (furthermore you will not be able to do it because your network domain is not supported, due to the "local" TLD
