Re: Looking for advice on next upgrade
It sounds to me that a Windows 2003 R2/Windows 2008 server Standard AD environment would be ideal for you. You can use GPOs to roll out software that you can create, have different policies for different machines. Your current local Group Policies can be automated via Group Policy.
I would recommend purchasing a Microsoft Press book for Windows 2003 server and/or 2008. Google also has a considerable amount of information.
The ideal would be to have 2 servers for redundancy but it depends on your budget. 1 server would probably be sufficient but not Best Practice.