Hi,
For a fresh installation of you may have to refer to
http://technet.microsoft.com/en-us/library/hh519664.aspx for manual configuration of remote SSRS. There is one more step (add a code segment to the rssrvpolicy.config) to complete compared to the Technet doc you used (upgrade guide).
According to the logs it may also be possible that there is a problem with the reporting account specified in the installation wizard. I assume 'VORDEFINIERT\VORDEFINIERT' is your anonymized reporting account right?
AssignSsrsRole Error: System.Web.Services.Protocols.SoapException : System.Web.Services.Protocols.SoapException: Der Benutzer- oder Gruppenname 'VORDEFINIERT\VORDEFINIERT' wurde nicht erkannt. ---> Microsoft.ReportingServices.Diagnostics.Utilities.UnknownUserNameException: Der Benutzer- oder Gruppenname 'VORDEFINIERT\VORDEFINIERT' wurde nicht erkannt.
bei Microsoft.ReportingServices.Library.ReportingService2005Impl.SetPolicies(String Item, Policy Policies, Guid batchId)
bei Microsoft.ReportingServices.WebServer.ReportingService2005.SetPolicies(String Item, Policy Policies)
StackTrace: bei System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
bei System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object parameters)
bei Microsoft.Reporting.Setup.ReportService.ReportingService2005.SetPolicies(String Item, Policy Policies)
bei Microsoft.Reporting.Setup.ReportingManagedCAs.AssignSsrsRole(Session session)
MSI (s) (DC:88) [18:41:27:769]: NOTE: custom action _AssignSdkAccountAsSsrsPublisher unexpectedly closed the hInstall handle (type MSIHANDLE) provided to it. The custom action should be fixed to not close that handle.
CustomAction _AssignSdkAccountAsSsrsPublisher returned actual error code 1603 (note this may not be 100% accurate if translation happened inside sandbox)
Hope this helps!