Creating a Project Workspace Template is easy. In the past I have been using STSADM commands to manage this. The issue is often the template is associated with a project schedule and thus fails to become a template. I just recently I found a few easy steps.

From Project Professional
1. Create a project called ‘Project Workspace Template”
2. Save Project
3. Publish Project which creates a project workspace called “Project Workspace Template”
From PWA
1. Delete the “Project Workspace Template” project but do not delete the associate project workspace. At this point, the association of the project workspace is freed and can be used as a template.
From “Project Workspace Template” Site
1. Customize the site as needed to meet your requirements
2. Load all the standard documents and templates in the Project Document Library
From Site Setting as site as a Template
1. Under the “Look and Feel” section; “Save the Site as a Template”
2. Once it is saved, it will appear in the selection of the EPT.
From PWA / Server Settings / Enterprise Project Types
1. Select the EPT to update
2. Under the Project Site Template, select the newly created template