A half a year of cash, at least. A year, preferably. Learned that from my folks when they had 4 boys going to $ school. That cushion seemed reasonable. Still seems so, 50 years later. You have your head screwed on straight. Yes, TV says otherwise, but consider the source.

I do very much the same as Marc. Customers know up front there are two kinds of code they get: Their code and my "library" code. The former is all theirs, and only theirs. Proprietary. The latter is for anyone. The customer can get the newest version years after I worked for them if they want it. I only deal with people who are not the sort of people who would sue about code, in any case. They have better things to do with their resources. For my part, I never, ever do contracts for outfits who compete with other outfits I've done contracts with. To me, it would be unethical to do so. Admittedly, "never, ever" doesn't apply to one organization which was and is so big they compete with everybody. In such a case, I must think of the organization as being only the tiny section/business unit I worked with.

rdiff-backup run every so often. As a practical matter, once a day while you are sleeping.

I wonder whether it would be better to make the chart's line fatter. Maybe with dithering around the edges to give even more sense of how noisy the original data is.

You do not type too emphatically. You are using the $5 keyboards that modern PCs and laptops are shipped with. You're screwing yourself every day. Every key you hit. Key caps on usable keyboards never lose their labels. Ever. Google around. There's a place that sells IBM 101's. pckeyboard.com. I don't like the little Return key on a 101, but YMMV. Taste. You may not like the short throw. You may not like the loud click. My current keyboard, the second in ~35 years, was made in 1991. The other keyboard I've used is an IBM AT board. It still works fine, but doesn't have F11, and you can't connect it to USB (draws too much power). There are good boards out there. Buy a real keyboard. If you're like most people here, you make your living with the thing. You could easily justify a buck a day for a good board just from how much better you'll type, not to mention how your hands won't be damaged. And yeah, you can pound a good board's keys. And yeah, turn it upside down and shake it ever few years. No harm done.

30, 40 years ago there weren't any young programmers, compared to today.