2003 server : adding an overseas notice, not sure how to set it up, two domains/one etc...

THis is mostly theoretical question:

Here is what I have

4 sites in the US, all part of one domain, lets call it "COMPANY.local" , I have an 2003 exchange server for mail and my users have "user@COMPANY.com" email addresses. Basic setup

right now my DHCP hands out DNS addresses of my two AD intergrated DNS servers in the US, lets say they are DNS1 and DNS2

Here is what I want to do:

We are adding a new office overseas, they will have their own servers, one 2003 DC and one 2003 exchange mail server also setup as a DC.

I want these users to also have "user@COMPANY.com" email addresses.

I don't care what domain they log into, can be the same or different.

I want to make sure that when I Lose an internet connection (unlikely but possible) that they can still get online through their own DNS and function fine.

I'd like to setup a 3rd AD intergrated dns server, DNS3 , and also a DHCP server for their subnet which will give all clients the IP address of the DNS3 server

Question that I have:

Are there going to be any issues with this???

can they simply be part of my current COMPANY.local domain ?

can I have DHCP give them their own DNS servers IP and not ours without any issues ? Do I just setup a forwarded for any unrecognized name to go to their ISP's DNS server?

will my clients in US be able to access their servers and vice versa?

Also, how do I setup the mail server? Simply as another exchange server and keep their mailboxes in that information store while I keep the US mailboxes on the US exchange server?

if I'm making no sense then please tell me how you would do it, I want them to be their own and fucntioning separate site if the US site goes down (as much as possible), internet must remain working for them , mail would not be so critical.