Domain Forest

I have several questions all of them related to the creation of a domain forest.
I have two domains and need to create a third one. I will take a W2K domain controller and demote it to stand alone so I can create the forest by making this machine a domain controller for the main domain that will authenticate users and computers. If the other two domains are resource domains, do I need to create user accounts in the resource domains? Or should I only use the domain local groups?
Is there any other configuration that has to take place in a domain forest other than the creation of transitive trusts from and to the resource domains?
I wish to simplify the configuration of the forest by only one DHCP server? (at the main authenticating domain). Do I need to use different subnets?
Do I need to configure a dns server in each domain or should I use the single dns in the main or master domain with the users?
Is there any other things to consider for this setup to work? I will have all users and computers logging on to the main domain and will create a dfs to simplify access to all the resource directories. I may have to map two shares (database applications).
Any advice is welcomed!