With a Project Plan 5 license, you are fully licensed to perform all of the actions of a Project Online administrator. These actions include creating custom fields and lookup tables, creating and editing enterprise calendars, creating and editing users, etc. To perform these actions, however, you will need to be added to the Administrators group in PWA.
You are also fully licensed to use the portfolio analysis tools in Project Web App. These tools appear in the Strategy section of the Quick Launch menu in PWA. If you do not see the Strategy section, you or your Project Online administrator will need to display them using the features on the Quick Launch page (accessed from the PWA Settings page). Hope this helps.