To sell or not to sell
Shalom and thank you for turning to us. It is heartwarming that Jewish practice in general and Shabbat in particular is so important to you that you are seeking creative ways of keeping this practice while not conflicting with your need to make a living. Your reasoning is quite logical, but nevertheless unfortunately it doesn't cut according to Jewish law. Truthfully Jewish law does have leeway and loopholes for many situations, since the Torah definitely takes the material needs and health needs of a Jew into account, as it states in Leviticus 19:5 "And you shall guard my laws and my statutes which shall be carried out by people and you shall live by them. I am the L-rd." One of the interpretations of this passage is that, as mentioned above, the Torah and mitzvot that a Jew performs should be in a manner which harmonizes with healthy and happy life in the physical world.
There are however cases that are more challenging, and this is one of them. The laws of the Sabbath are complex and require much study, but one thing I must explain here is that what Halacha – Jewish law, calls 'work' on the Sabbath doesn't really have anything to do with expending effort. So while sitting with a cup of coffee IS a fine thing to do on Shabbat, arranging business transactions, even by proxy, is not. Using your cellphone or computer are among the things that are not part of Sabbath practice. The actions we don't do on Shabbat stem from thirty-nine prototype labours that were performed by the Jews in the desert to build the sanctuary in which the Jewish people were to serve G-d. In every generation questions arise about new conditions and scholars have to assess, according to special principles that were handed down together with the Torah, how the law applies to the varying conditions. In hospitals there are many leniencies about Sabbath practice but nevertheless the law is kept (in hospitals run by orthodox Jews) and there are ways to do it. In your case, it seems you will have to be even more creative than you already have been. Perhaps you can try to arrange your transactions for Friday late afternoon when people are home from work but before the onset of the Sabbath, (provided you have a way to get home in time to observe the Sabbath properly at home,) and/or do some transactions on the evening after the Shabbat 'goes out'. (For the exact times of the onset of Shabbat and the end,as well as practical guides to keeping Shabbat, you can look up Chabad.org.) There are frameworks in which a non-Jew works for a Jew on Shabbat but again the laws are complex and firstly, it does not seem to apply to your situation, and secondly, it must be done according to the instructions of a competent orthodox Rabbi who has been informed of the exact relevant details of the situation.
I would like to share a true story with you about a Jew who stood up to the test and challenge of keeping the Sabbath despite obstacles. It happened to my Rabbi's great-grandfather.
At the turn of the previous century the immigrant family arrived, like many others, to the shores of Ellis island, and like many other Jews fleeing the progroms of Europe, the head of the family sought work every Monday morning again, because every Friday he was fired for not wanting to work on the Sabbath. Eventually the family had to move to a coal cellar. One day a Jew who had immigrated in an earlier wave of immigration was walking down a New York street, and he saw two 'black' children playing on the sidewalk. As he approached them he noticed that they were speaking Yiddish! Surprised, he scrutinized them and suddenly realized that these were not African-American children, but children of European origin who were black all over with soot. He began conversing with them and they explained that they lived in a coal cellar. He asked to see it and they brought him 'home' with them. This Jew had become wealthy while adopting a secular American lifestyle. When he saw the difficult conditions in the coal cellar, he pulled out a check book and immediately wrote a check for a sizeable amount that would enable the family to rent a normal apartment.
The children's mother asked the kind man if he worked on Shabbat. In embarrassment the man admitted that he did. The mother refused to make use of money that had been earned on the Sabbath. I have not heard that thereafter the children found a big treasure amongst the coals, but I do know that they survived, and their descendant is my Rabbi.I think that the would-be donor also returned to keeping Shabbat as he had done in his youth in Europe. Today there are many famous professional sports players, politicians, actors and more, who refuse to accept jobs that involve transgressing the Sabbath. In modern times this is often well-received.
Keeping the Sabbath according to Jewish law is something that will help bring us closer to Messianic times when evil will be wiped off the face of the earth, as the prophet Michah (ch.4:3-4) said "nation shall not lift a sword against nation nor engage anymore in war strategies, and they shall sit each one under his vine and under his fig tree and no one shall cause terror because the mouth of the L-rd of Hosts has spoken."
The sages of the Talmud say that G-d promises: "If you keep (the mitzvah of) Sabbath candles, I will show you the lights of Zion." In other words, keeping the Sabbath properly can bring about the Redemption! Sometimes when you take a leap of faith and act upon it – you do see miracles!