Where To Go Next
Walk before you run, though. Practice making simple "console applications" like <code>p.exe</code> above. The XMingwin distribution comes with a rich set of tools, going far beyond basic compilation. Your customers' needs might take you next to creating deployable libraries (the DLLs of the Windows world), or perhaps graphical user interface (GUI) applications. Maybe you'll need to "build out" your factory to exploit third-party libraries.
In any case, you should be able to find any resources you need for these tasks through a page I've set up to answer questions about XMingwin.