My company is planning on developing for Windows Phone 7. The build server we have, however runs Windows Server 2008. According to the Windows Phone SDK release notes I\'ve
Most the issues of this nature come into play meeting the emulator's requirements rather than the development tools.
With that said some are hacking around the walls put up to stop people going into the unsupported territory of WS2008.
Judging by your requirements I'd say dive in. If you have the option to test on device or in emulators in Win7, that will place you well.
This post likely of interest.
Aaron Stebner's WebLog : How to install the Windows Phone Developer Tools CTP Refresh on Windows Server 2008