Evaluation: Keeping audio consistent across multiple tracks?

https://www.youtube.com/watch?v=NhanZZYr0d8

This is the video I made for media studies at my high school. The one thing that is killing me about it is the audio being inconsistent - not in volume (I normalized everything to -12dB), but, I think, in frequency and bassiness. The subject was speaking quieter when we shot his close-up, and louder when we shot the medium; I'm pretty sure this is the problem.

Also I've only recently had access to decent sound recording equipment, so I'm very new in terms of audio editing, and any tips to fix audio issues or in terms of workflow would be greatly appreciated.

Thanks a ton in advance.