1. Nothing special needs to be done to use multiple files. All .brs files in your source directory are compiled together.
2. The entry point is RunUserInterface. If there is no such function, it uses Main. If the channel has a screensaver, there are one or two special entry points, RunScreenSaver to run the screen saver, and RunScreenSaverSettings to run the settings screen for the screen saver, if there is one.