There are two things you should consider when you have lots of classes and header files in you project;
1- in header files, try not to include other header files, instead try forward declaration, or better to say, first use forward declaration, if not possible, use include.
2 - do all necessary includes in your ".C" and ".CPP" files instead.
How to "know" if you can use forward declaration? The answer is easy;
If all you have in your class header file, are references and pointers to a class, then only use forward declaration for that class.
On the other hand, if an instance of a class is created in the header file, or if you are inheriting a class from another, then the class header file must be included. To prevent this, try passing object by reference and pointers as much as possible...