Your overall class design will show you if you will end up with protected members or not. Whether you make them private, protected or public, that isn't something thats chiseled in the stone, so feel free to create your class tree without much thinking about that. If at first you don't know if the member will be used by derived class, and in what way, you'll surely find out when coding.
Most important thing to decide is what is public vs /private, because that's the way you present your class to the outside world.
