Advice on how to proceed?

My Network consisted of a few domains. For the most part, if there is Domain
A, B, C, D, and E.....Domain A is pretty much the one that is primarily used
by everyone with the other Domains with very few members on them. So, on
Domain A, It is a NT Domain with 3 BDC's and 1 PDC. 2 of the BDC's are
Exchange 5.5 Servers. Most, I would say 85% of the rest of the Member
Servers are either 2000 or 2003 Servers already with a few NT Servers still
left behind.

What I did. I popped a 2000 Server CD into my PDC and upgraded it to 2000
and Active Directory. Went pretty smoothly. So now is where I am stuck. How
do I proceed from here. Now Domain A is Domain, which is because
Active Directory. So now I am sitting in Mixed Mode, PDC is 2000 Server
with Active Directory and my my BDC's sitting with NT and Exchange 5.5
running on them.

So any advice on how to proceed from here and complete this migration would
be excellent or some sites I can go look at with White Papers to help would
be nice.

I guess my questions are, it seems most of the machines are appearing in
the Active Directory, so as far as User Accounts go or Machines, do I need
to do any right?? Because I did a in place upgrade??

Is my next step upgrading the BDC's to 2000 as Domain Controllers? Will
Exchange 5.5 continue to run if I upgrade them to 2000?? If I upgrade my
BDC's to 2000....then Domain A is Active Directory can I take it out of
Mixed Mode to Native Mode? Will this affect the other Domains that are out
there?? How can I bring them over under my Active Directory Forest? Or do I
even need to do that??

Thanks for any help.