High-performance detectors with high spatial and time resolutions are required in applications such as imaging of fast processes, time-resolved coherent scattering, and time-resolved X-ray spectroscopy. Recently a new type of X-ray detector was proposed, based on microchannel plates (MCP) coated with resistive and emissive layers inside the pores by using atomic-layer deposition with better functional optimizations. Two microscopic Monte Carlo codes were used to calculate the characteristics of secondary electrons emitted from a photocathode irradiated by X-rays with energies of 1-15 keV and by electrons with energies in the interval of 0- -2 keV. WO3 was selected as the photocathode and the electron emissive material. The emissive characteristics obtained by the microscopic Monte Carlo codes were used as input data for a third, macroscopic MCP simulation Monte Carlo code, for calculating the gain and transit time spread of a MCP-based X-ray detector. Our simulation results showed that the X-ray detector should improve the spatial and time resolution and push the development of high-quantum-yield photocathodes based on MCPs.