What is the ruling on women visiting graves, and is there evidence for that from the Quran and Sunnah? And do the spouses incur an expiation, or is the marriage contract void, if the wife states at the time of the marriage contract that she has received the dower, when she has not yet received it, with the husband intending to deliver it to her?

It is permissible for a woman to visit graves, provided she adheres to Islamic guidelines. The dowry (Mahr) is a right of the woman, and it is not a condition for it to be handed over at the time of the contract, nor for it to be mentioned therein. If a man contracts marriage with a woman without mentioning the dowry, she is entitled to the dowry of her peers if he consummates the marriage with her, or to whatever satisfies her. The marriage is valid if the orphan girl is an adult, and expiation for lying is by seeking forgiveness (Istighfar).