I have a question on khums on business capital. I'm in the car industry and we buy and sell vehicles. Do we pay khums on the money that's in the business that's used as capital to purchase vehicles? If we do and the following year the capital in the business increases to have more purchasing power, do we pay khums on the extra amount of capital?

Yes, the Khums applies to the business capital that’s used to purchase vehicles (unless this capital is from money that you have already paid Khums on, then the Khums wouldn’t apply).
Now if the value of the capital increases next year, you would pay khums on the increase.