Is thinking about seeing God, heaven, and Prophet Muhammad, and about how God created the world, while believing in God and His oneness, considered unlawful (haram)?

If the wish is to see Allah and His Messenger in the Afterlife, then it is commendable, and its means are faith and righteous deeds. As for wishing to see them while awake in this world, that is wishing for the impossible and exceeding limits in supplication. However, loving to see them in a dream is permissible.