I would like to ask about doing a mutah with a Hindu who is ready to convert for doing this mutah but not permanently. He will remain Muslim till the end of mutah. What if he agrees to convert to Islam for good then am I allowed to do mutah with him. If he doesn’t and I know he is converting temporarily then am I allowed?

Not allowed, except if you are confident that he is really permanently converting to Islam.
Do not sell your self.