Is it permissible to proceed with a marriage (literally, "marry by religion" or "marry for the sake of religion") given the fiancé's financial struggles, or is it better to postpone the marriage until money becomes available, knowing that he intends to borrow from his brother and might ask him for money without prior notice?

Islam encourages marriage and promptness in it when a young man is able, especially if he fears falling into haram (unlawful acts). It is permissible to take a loan for marriage to preserve one's chastity, and Allah will aid the husband and enrich him from His bounty. However, if the young man does not fear for himself or fears inability to repay, it is better for him to wait until Allah facilitates his affair. It must be noted that the fiancé is a stranger to the fiancée until the valid marriage contract is concluded. Therefore, he is not permitted to be alone with her or to see what a stranger is not permitted to see.