You can use the Asset Transfer  tool in CJA to select the workspace projects that you'd like to transfer ownership.  Future iterations of the AA Component Migration tool may incorporate asset transfer into the workflow.  Admin users were chosen for the AA->CJA migration to mitigate permissions issue...

The Reporting APIs documentation provides some guidance on using the /reports and /topitems endpoints, including examples.  There is also additional documentation on breakdowns and migrating from the 1.4 to 2.0 APIs.  You can use the debugger in Analysis Workspace to see how it uses the 2.0 APIs for...