DNS and DHCP

In a few days I will be installing a fresh copy of 2012 Standard on a new server and creating a new domain.  I will be configuring DNS and DHCP.  I have a few questions below and would appreciate some help, thanks:

1.  I have 2 other older servers running 2003.  I know I should have at least 1 secondary DNS, but should I make a 3rd Just in case?

2.  When setting initial network settings for DC and Primary DNS server, what should i enter for DNS servers?  Just 127.0.0.1 or should I add alternate (2nd/3rd DNS server)?

3.  When configuring DHCP, from what I've read, I should only include internal DNS servers for clients and then use Forwarders for queries not found locally.  First, is this the best method and second, what if for some crazy reason all DNS servers are down, how will clients access internet?

4. (not DNS/DCHP related)  I am trying to start this network from scratch as my current setup is such a mess.  The 2 older 2003 servers are currently part of the same domain.  The domain I am creating under 2012 will be completely new (new name).  I plan to configure this new domain first, and the do fresh installs of 2003 on the other 2 serves as they are having issues and then add them to the domain as secondary controllers.  

Will these 2003 servers be easily added to the 2012 domain or with there be any compatibility issues I should be aware of?  

Thanks