Catherine Heszer, Professor of Jewish Studies at the University of London, has estimated that the literacy rate of Palestine in the 1st century was about 3 percent.
Only young men from wealthy families could read and study the Torah, and in 1st-century Palestine very few families were wealthy. We might as well say that today, young men and women enter medical school to become brain surgeons, so the majority of people are qualified to remove brain tumors.
A tax collector in ancient times was not like today's IRS agent with a CPA. Matthew was more of a toll-booth collector, and one merely need to be able to perform simple counting and making change to do that. When Matthew met Jesus, he was sitting at his toll booth (Matthew 9:9). Lots more about Matthew
here.
Being fishermen does not mean "running a fishing business" which invokes today's imagery of keeping detailed records and reading complicated regulatory papers. It means getting in a boat, netting fish, carrying it back to a market, and selling it to others. You imagine Peter and James were captains of industry? Peter and John admit outright in the Book of Acts that they were unlettered.
When I was a Christian, I was told that part of Jesus' appeal was that he spent his time with the poor, the downtrodden, the lowest classes of people. But if we need Jesus to move among the circles of the
wealthy elites in order to build up our case that Christianity is authentic, that's fine too. But it can't be supported biblically.