Did the Prophet (peace be upon him) diminish the status of Mu'awiyah by saying: "He is a صعلوك with no wealth," and does this imply an invitation to prefer the wealthy and seek worldly possessions?

The hadith contains neither a disparagement of Mu'awiyah nor an invitation to worldliness. Rather, it is an encouragement to choose a man capable of providing financially. The Prophet was a consultant and a trustee, so he advised Fatimah with what he deemed suitable for her, as Mu'awiyah was poor at that time, and thus he forbade her from marrying him. This indicates that a consultant is entrusted.