Hello,
1. Considering SQL Server 2014 Express, both Windows Server 2012 R2 and Windows 7 SP1 Professional x64, are supported. I need virtual machine for SQL Server ONLY. Does it make sense to pay more for Windows Server? Would it be faster, better, _really_ more reliable then Windows 7 (or 8.1 or any other non-server OS)?
2. It is not recommended to install SQL Server on domain controller, although cheapest server version, Essentials, requires to be a DC. We has less then 20 users, there are roaming profiles in use (hosted by separate file server) and beside rights management DC has nothing more to do, while having plenty of RAM and CPU resources to use. Would it _really_ be a problem to have SQL Server on such DC?