Question
As follow up, I thought for havdalah drink and the drink for Saturday kiddush, a chamar Medina (such as etrog liqueur) is permitted (not for Friday evening shabbat). Secondly, is the principle of using a mitzvah object for another mitzvah an optional mitzvah, a chiyuv, or merely a minhag?

Question
The Talmud/gemara in I believe Shabbat 117b states you should use something for a mitzvah for another mitzvah. Would using leftover etrogim from Sukkot to make wine for kiddush and havdalah fall under this category?

Question
What are the restrictions regarding modern convivences which have become part of daily life in the past 150 years e.g. telephones, cars, stoves etc. Who in the Jewish community, invited appliance corporations to decide that stoves should replace personal control over how Sabbat is observed.