I don't know much about SDE, but I think the standard order is Desktop, Server, then SDE. And I believe you can just use Desktop aand SDE.
To publish a service from ArcGIS for Desktop 10.1, you will need to either publish to ArcGIS for Server 10.1 or ArcGIS Online.
Enterprise geodatabases are supported in 64-bit database management systems
As mentioned in What's new in ArcGIS 10.1 for Server, ArcGIS for Server is now a 64-bit applicatiion. ArcSDE and enterprise geodatabases are part of ArcGIS for Server and, at 10.1, support only 64-bit databases. See the topics in the Relational Database Management Systems section of the ArcGIS 10.1 System Requirements for supported databases and operating systems.