Leave the work to PCB plant. You don’t need to spend your time by designing stackup. Leave it on Chinese PCB manufacturer – they are professionals. They do it every day. Also, by doing it this way, you can work on design in parallel of handling issues with PCB stackup.
Many times PCB manufacturer is not able to build PCB stackup designed by other company or a person outside their company. The main reason is unavailability of material used in some PCB stackups. Selection of material is the best to leave on them – they will choose stocked material.
China printed circuit board suppliers use different track geometry calculators and they will not guarantee track impedance if track geometry is calculated by someone else. Many times their calculated numbers and your calculated numbers will be different.