There is no essential reading for Module 7. The recommended readings would be helpful, but if you are short on time then you could skip the readings for this module spend your time on Module 8 instead.
Reading
King: A beginners’ guide to statistical parametric speech synthesis
A deliberately gentle, non-technical introduction to the topic. Every item in the small and carefully-chosen bibliography is worth following up.
Zen, Black & Tokuda: Statistical parametric speech synthesis
A review article that makes some useful connections between HMM-based speech synthesis and unit selection.
Taylor – Chapter 15 – Hidden-Markov-model synthesis
Written with a traditional "starting from automatic speech recognition" viewpoint, you will need to make the connections for yourself to the more general concept of text-to-speech as a regression problem.
Qian et al: A Unified Trajectory Tiling Approach to High Quality Speech Rendering
The term "trajectory tiling" means that trajectories from a statistical model (HMMs in this case) are not input to a vocoder, but are "covered over" or "tiled" with waveform fragments.
Pollet & Breen: Synthesis by Generation and Concatenation of Multiform Segments
Another way to combine waveform concatenation and SPSS is to alternate between waveform fragments and vocoder-generated waveforms.