Do I need a BDC when upgrading an existing NT 4 domain?

I currently have a PDC and a BDC, and both are running Windows NT. The PDC is also the Exchange server (5.5).

I want to basically start over with a new server running Windows 2003 and Exchange 2003. Both of the existing DC's won't really be needed or required after my upgrade. What is the best way to get the new machine into the domain? Or would it be easier to create a new domain and add the clients to it? There are about 30 workstations in the domain. Will the new server be a PDC or will it use AD? Do I really need a BDC? If I do need a BDC, could I use the existing NT machine?
If you are upgrading an existing NT 4 domain, you'll need to start with the existing PDC, then upgrade any remaining BDCs. Computer and user accounts will be migrated during the upgrade process. If you wish to start over from scratch with a brand new domain, you'll need to recreate all user and computer accounts and rights assignments. Also, the NT4 controllers will need to be re-installed in order to add them to a different domain. See https://searchwindowsserver.techtarget.com/news/880148/Dos-and-donts-of-Active-Directory-migrations-part-2 for a brief overview of the Active Directory update process.