Found out that even before doing the install of a 3rd-party app on Win 8.x, I'll need to set a GPO to allow this action. Apparently best practice is to enable the "Allow all trusted apps to install" GPO, load the app via PowerShell, then disable the GPO. Also appears that I have to set some execution policy as well.
Thinking maybe the easiest would be to put everything in a batch file but not sure how to detect when the metro-style app install is done before disabling the GPO. Am I headed in the right direction or is there a better way of getting this done?