What is the religious ruling on a woman marrying without a guardian (wali)? Is it permissible for a woman to appoint someone other than her father as her guardian? What is the minimum amount that can be offered as a dowry (mahr)? And is using a condom to prevent pregnancy after marriage considered a sin?

You should supplicate and implore Allah to facilitate marriage to a righteous woman. The guardian (wali) is a condition for the validity of the marriage, according to the preponderant opinion, and a woman's marriage without her guardian's permission is invalid. Merely informing the girl's guardian of the marriage is not sufficient; rather, the guardian or his representative must be present at the marriage ceremony, and the father is the foremost among guardians. The dowry (sadaq) is obligatory in marriage, and no specific type or amount is stipulated for it. Complete prevention of procreation is not permissible except out of necessity, and it should not be temporarily prevented without need; it is a right for both spouses. If marriage to this girl is facilitated through a lawful means, then all praise is due to Allah; otherwise, seek another and avoid arousal-inducing stimuli until marriage is achieved.