ok, just a quick question on child DCs. Should I setup dns on the child DC before creating the child domain or is it ok to just point it at the parent dc for dns?

If you point to the parent DC, a subfolder will be created in the zone which will store all related DNS records for the child domain. From a technical perspective, this is absolutely OK and will provide name resolution services for clients. However, you need to decide who will manage DNS for the child domain? Do you want the records for both domains in the same zone? Any security concerns?Visit: anITKB.com, an IT Knowledge Base.

It's depends on requirement. It's fine to either set a DNS on child DC or using DNS on host. If they are not in a same zone and/or network speed is low (or network traffic is heavy), you will need to set a DNS on child DC.Shaon Shan| TechNet Subscriber Support in forum| If you have any feedback on our support, please contact tngfb@microsoft.com