I would not disagree that you can do it, but I am skeptical that you can do it in 5 years.
Honda did develop their HF118 turbofan engine apparently from scratch, but it took about 8 years [1]. And for the actual commercialization they teamed up with GE and then it took another 10 years until certification of the successor HF120 [2].
[1] scroll down on https://global.honda/en/tech/eVTOL_gas_turbine_hybrid_system...