Is it better for a middle-income family for the husband to take out a loan to buy an apartment, or to marry a wealthy woman to improve their standard of living, while desiring to live in a permissible manner?

There is no harm in a husband's desire to marry a wealthy woman, based on the Prophet's (peace be upon him) saying: "A woman is married for four reasons: for her wealth, for her lineage, for her beauty, and for her religion. So, seek the one who is religious, and you will prosper." However, he is not permitted to take her money unless she willingly consents, based on the Prophet's (peace be upon him) saying: "The wealth of a Muslim is not lawful except with his willing consent." As for a loan, there is no objection to it if it is a good, non-interest-bearing loan. Your husband should seek Allah's guidance (perform Istikhara) regarding this. An interest-bearing loan is not permissible except in cases of dire necessity.