Shutting down Exchange in linked mailbox environment

Hi

In our environment, we have an Authentication forest (AuthAD) and a messaging resource forest (MessAD).

In one of our sites, we are going to have some maintenence carried out to the Data Center, this means we'll need to shut down all servers. This site contains:

3 x AuthAD GC's
3 x MessAD GC's
1 x Exchange 2007 SCC Cluster
2 x Hub Transport Exchange 2007
2 x CAS server Exchange 2007
2 x UNIX DNS

AD is used for DNS in MessAD, but AuthAD uses UNIX DNS.

My questions:

1. Will the shutdown of AuthAD GC's have any effect on Exchange?

2. Do ALL GC's have to be shut down last, or can some be shut down first as long as there are still some remaining right at the end?

3. In which order should the Mailbox, Hub and CAS servers be shut down / powered up?

4. All when powered on, let's say two MessAD GC's are powered on at the start, they replicate all data from another site, then we power on Exchange. Finally, we power on the last GC. Obviously, this GC is lagging behind in terms of new data, what would happen if Exchange chose that GC as one of it's own? How does Exchange know to connect to the most up to date GC?