Building a business app using PHP-Gtk2

Hi, I am new to PHP GTK. I have been a PHP developer for several years and now I am looking for a way to use my PHP knowledge for writing desktop apps, and found GTK. I do like PHP GTK so far, I installed it and tried generating some test apps from the manual, and it worked great. Now I would like the opinion of more experienced users, to see if PHP GTK is suitable for a given project. There is an old business app with several modules (Invoicing, Products, Customers, Inventory, for example) which I coded years ago in Clipper for DOS. Now the company wants to port it to a Windows app. Is PHP GTK a good choice to build such an app? The source code will spawn through multiple source files, do I have a way to load parts of the app in memory at a time? For example if user goes to Customers menu, app should load the source code files for the Customers area and display those windows, ignoring all windows for Inventory and Invoicing area. I guess I am mainly asking about possibilities for applications architecture, because all examples I have found so far are small apps consisting of just 1 source code file and 1 window. Thanks for your help. Regards, Veronica