In general, either “to” or “for” can be used in the two sets of prepositional phrases you presented above. The choice will depend on your intent as speaker or writer in making the statement. In the case of “letters to/for you,” use “to” when you have in mind “you” as the specific addressee or recipient, as in “These letters are addressed to you.” On the other hand, use “for” when you have in mind “you” as the object of the message contained in the letters, as in “I was told that this bunch of letters is for you.” The same distinctions apply to the other sets of prepositional phrases you presented.
Just keep in mind that the prepositions have specific functions in language. In the case of “to,” among several other functions, it indicates a movement or an action or condition suggestive of movement toward a place, person, or thing reached. In the case of “for,” also among several other functions, it indicates purpose or the object or recipient of a perception, desire, or activity. It’s your call as a writer or speaker which of them to use depending on the precise sense you want to communicate.
