Preferred and Secondary DNS servers on single 2012r2 DC with AD,DNS and DHCP

Hello All, I hope this isn't too easy or a repetitive question. One weak area I have is understanding how to configure DNS on a domain controller -the only DC on a network. It has the AD and DNS and we made it the DHCP server. OS is 2012r2. Let me explain what configurations I have on the server and router...  We have a static IP address on a SonicWALL router, configured with the ISP DNS servers. Now - here's one possible fault... I have teamed the NICs on the server (2), just the standard options.... I think I have read somewhere that may not be a good idea on a DNS server... not sure... So the teamed NICs have the servers IP address on the LAN assigned. I have server set up to use root hint servers and no forwarders and the root hint servers are resolving. I am using the ISP primary DNS as preferred DNS server on the DC NIC (teamed), for the secondary I am using the DC's LAN IP address - versus the loopback address...  I am away from the site at the moment but will go onsite soon. I have read a lot of stuff lately and its pretty diverse... meaning different opinions for similar circumstances others have had. Do I need to get rid of the ISP's DNS server in the DC LAN properties altogether? Using root hints, if it matters to next question, what would  use for the Primary and Secondary DNS servers in the DC's NIC properties then? I have read - use the DC's IP address as the first (primary).... I just need an answer I can feel good about - and I will wait to be at the server before I make a change so I don't knock down the network from afar.

Errors - I run the BPA on AD and DNS and I get errors in both - the DNS seems easy to interpret - complains about the ISP external DNS server unable to resolve internal records etc... and AD is reporting issues with advertising and registering DNS records and other advertisement such as LDAP and PDC for the domain....  I think if I can get the DNS sorted out on preferred / secondary on the DC then some of this will clear up. I ran dcdiag /test:dns and got a lot of the same DNS errors reported. We migrated a Server 2003 DC to this one a couple years ago and I also have my concerns about all the stuff I still see in AD that belonged to the old 2003 server, like old SQL version entries etc...  and that's another topic for later perhaps...  

As for Internet access for the computers on the domain and the server - I don't see any real issues there but I do see where access shares over the network  - has become spotty and I am starting with the server - clean it up and then see how shares are across the LAN.  Again.... thank you for your time and assistance.