I need to write a .NET client app that accesses Project Server 2013. I.e. PWA. That client app must run on Windows 7 workstations. I plan to use Project Server Client Side Object Model (CSOM) to access all the projects, tasks, resources, and assignments in Project Server.
Q1: Can I sign up for Project Online and use it to test my client app?
Q2: Will it act exactly like the on-premise installations of PWA?
Q3: If my client app works with Project Online, will it likely work with on-premise PWA installations?
Q1: Can I sign up for Project Online and use it to test my client app?
Yes, just go ahead and setup your Office 365 development environment.
Q2: Will it act exactly like the on-premise installations of PWA?
In respect to CSOM API, yes.
Q3: If my client app works with Project Online, will it likely work with on-premise PWA installations?
Yes. However, on-premise SharePoint (and Project Server) deployments have to be configured to allow access by an App for SharePoint using CSOM.