Terahertz (THz) integrated sensing and communication (ISAC) with multiple-input multiple-output (MIMO) architecture is recognized as a promising interdisciplinary technology for ultra-high-rate mobile communications since the systems enable narrow beam tracking which is necessary in the THz band. In this work, a link-level simulator for THz MIMO ISAC in time-division duplex (TDD) operation is proposed to design and analyze mobile systems. Compared to the simulators in the literature, the proposed simulator is more practical and comprehensive, employing two-dimensional position and motion simulation to develop localization capabilities, and considering THz characteristics such as wideband echo, molecular absorption and cluster-based channel. Specifically, the simulator supports the standard orthogonal frequency division multiplexing (OFDM) and discrete Fourier transform spread OFDM (DFT-s-OFDM) waveforms for sensing and communication simultaneously. Trade-offs between communication and sensing metrics required for waveform numerology design are investigated. In particular, by exploiting TDD framework's integration capability, range-velocity-angle estimation with virtual array and sensing-aided downlink spatial multiplexing are co-designed. Additionally, a user interface with elaborate parameter configuration is introduced. Finally, we implement an urban vehicle-to-vehicle (V2V) application case to verify the simulator. The simulation results present the feasibility of the developed integrated architecture.