What is the proper way to deal with auspicious and warning visions, and is it permissible to interpret someone else's vision without religious knowledge, or to act based on a vision that sets an example or carries information, and does that affect the validity of the deed or the intention?

A dream is a part of prophethood, and it is not permissible to be lenient in interpreting it without knowledge. Some jurists have even stipulated that it is forbidden for someone who does not know the principles of interpretation to do so, whether the dreamer requested its interpretation or not. As for the dreamer acting upon what they understood of a lesson or advice from their dream, there is no harm in it as long as it aligns with the objectives of Sharia, and this has no connection to polytheism nor does it affect the intention or validity of good deeds.