Problem 1: As an Egyptian teacher working at an international school, where the speaking environment should be in English, I, students, and others used to address other teachers with the titles Mr. (his name) and Ms. (her name). I know that the title Ms. pronounces /mɪz/, but actually almost all of us used to say it /mɪs/.
Question 1: Is it correct to pronounce it that way (using S sound, not Z sound)?
Problem 2: In writing, I know we shouldn't end a sentence with a contraction (or a weak form); so when texting a male teacher, I may write something like "thanks a lot mister," and when texting a female teacher, I may write "thanks a lot miss" (even if she's married).
Question 2: Is miss here proper? Does it serve the same meaning as Ms.? If not, then what is the full form of Ms. to end the sentence properly?
Problem 3: I told my students something like the following sentence: "Ask any mister or mistress before you do that."
Question 3: Is the usage of mistress here correct? Because I just checked a dictionary and found that it's an old fashioned word that has a different meaning now.