Take a look at this I posted in another thread and don’t forget you could have each window’s code in separate file(s) and then using XIncludeFile to inject the code where you want it in your larger program.
If you’re going to use PB’s Form Designer tool you’ll probably want to uncheck the option to generate an event loop and keep the code it generates in a separate file so you can edit / regenerate your form’s layout without affecting any other code.