Is it permissible for me to keep the house that I built with a usurious loan after paying off the loan by selling land I inherited, and is Zakat obligatory on the money resulting from the sale of the inherited land, and what is its amount if it is obligatory?

Repentance is obligatory for taking a usurious loan, and the borrowed money must be returned. However, the interest should not be returned if possible. If accelerating the repayment leads to the waiver of interest, then proceed with that. There is no sin in keeping a house built with a usurious loan. There is no zakat on inherited money until a year passes and it reaches the nisab, unless the deceased did not pay his obligatory zakat before his death, in which case the heir must pay it.