Windows Server 2008 Domain Role Assignments with DC in HyperV VM

Our current environment is this:

1. Single domain with three (3) DCs, all GC servers.

2. First DC is running Windows Server 2008 Standard SP2 32-bit. Machine is generic black box with P4 and 4GB of RAM.
3. Second DC is running Windows Server 2008 Standard SP2 32-bit. Machine is IBM System x3250 with dual core Xeon and mirrored 73GB drives.
4. Third DC is running Windows Server 2008 R2 Standard SP1 64-bit as a VM inside HyperV. 4GB allocated to it.

5. First DC is DNS and Print Server. (with GC)
6. Second DC is DNS and DHCP Server. (with GC)
7. Third DC is just DC (with GC) so far.

I have a separate VM that will be the new print server, so I intend to remove that first from the First DC.

Here are the current roles:
First DC - Schema Master, Domain Naming Master, Infrastructure Master
Second DC - PDC, RID Pool Manager

We have just these DCs. All servers in the organization are Windows Server 2008 or 2008 R2. All clients are Windows 7.  We have about 80 users - not a very big environment.

Questions:
1. I intend to retire the First DC.  How should I split roles between Second DC and Third DC (VM) ?
2. I intend to install DNS on Third DC (VM).  Is 4GB and two virtual processors allocated to it sufficient to support DNS with additional roles suggested above ?

Thanks much.
-Stephen