Is it May a good weather in Inner Mongolia?

Yeah, I think so. It will be pleasant and comfortable in May, with the lowest temp of 13C and the highest one of 26C. It may rain a little, when you may feel a little cool.
However, if you wanna see grassland there, May is a little early and July shall be the best season.

Yes,but you may want to keep track of time because at the end of may it is rainning season Good luck