1. Yes she can create a mess by withdrawing her consent from mutual divorce the court may not grant you divorce. Then further you need to challenge said order and establish before court that your wife just for sake of enhancing monetary gains has withdrawn the mutual consent which amount to further cruelty. the high court may then grant you divorce a similar case came up before Rajasthan High court where the court gave divorce to husband when wife withdraw consent in mutual divorce.
2. The best thing is agree to her unreasonable demand buy the land and end this episode. you can make a supplementary agreement if further she changes her mind you can file a petition before the high court.
3. yes kid can ask maintenance from you.
4. See if it is self acquired property no one other then you has any right in property you can alienate property on you wish. you can sell gift property on your wish. Further child will have share in the ancestral property.
see if kid in future he files for maintennace you can contest same that wife was given amount for maintenance of kid.