I see that you have successfully installed the ASDK and have run the validation tool using test-azurestack.
If all of the test-azurestack comes back as passed, I would first make sure that the VMs are not being created first. For the error - 'Guest agent Not Ready. VM agent is not ready', your VM will still exist and be running in some cases, have you tried to RDP / SSH into the VMs?
As for the 'DISKS' error, I have not seen this in the ASDK environment where test-azurestack also comes back as passed. Can you try to run test-azurestack again to see if there is another issue?
In most situations for errors like this where the VM is not being properly created, the end solution is to reinstall the ASDK. Troubleshooting and running test can take a long time, so typically I would recommend a reinstall using the latest version.