How hard is it to take 5 4 credit courses in one semester?

I wouldn't do it, but then again it depends on the difficulty of the classes and how interested you are in them. Last semester I took 18 credits and nearly died from the stress of studying, and fall semester I took the same amount of credits and nearly died of boredom because it was so easy. If you are a good student and typically do well in those areas, go for it and challenge yourself!