In order to comprehensively utilize ocean resources and renewable energy, a novel modular floating structure (MFS) system with multi-direction expansibility has been proposed, which includes inner hexagonal tension leg platform (TLP) modules and outermost floating artificial reef modules coupled with the function of the wave energy converter (WEC). Considering both the hydrodynamic interaction effect and the mechanical coupling effect, the main dynamic responses of the MFS system have been analyzed under different incident wave directions, and the corresponding physical mechanism has been clarified. Results indicate that connector loads slightly increase, but motion responses of the MFS system are more stable when the outermost floating artificial reefs serve as the up-wave modules. Outermost floating artificial reef modules have shown good wave-attenuation capacity for inner TLP modules, as well as producing considerable output wave power. The effect of key power take-off (PTO) parameters on the WECs’ performance has been investigated, and the optimal PTO damping coefficient has been suggested. In addition, extreme responses of the proposed MFS system have been further studied, and its safety has been well verified under typical extreme sea conditions. The main results of this work can serve as a helpful reference for the construction of future offshore floating cities.