Is the thought that good deeds might be rewarded only in this world, and that one's fate after death might be torment and Hell, contradictory to having a good opinion of Allah? And is this thought commendable, or is it impermissible? What should a person do about it?

Commendable fear is that which motivates good deeds and prevents its possessor from Allah's prohibitions. As for fear that leads to depression, negligence in good deeds, or doubt, it is not the desired fear. Fear is not an end in itself; rather, it is a means and disappears when the feared thing no longer exists. Sincere fear is abstaining from sins. Diligence in obedience and having a good opinion of Allah indicate a balanced scale of fear and hope.