If any of those 30 years of programming was in C or C++, then you probably have been exposed to the standard technique of breaking large projects in to .h / .cpp / .c files. That provides a lot more control and modularity than the "Arduino Way" of using multiple .ino files. When you do that, the IDE simply mashes all the .ino files into one big compilation unit and hands it to the compiler. Really not modular at all. See my Post #5 here.