What ratio and time for cold brew that does not taste harsh?
1:8 coffee to water by weight for a concentrate, 16 to 18 hours in the fridge, coarse grind. Harshness at that ratio is usually grind size rather than time: too fine and you over-extract even cold.
How do I plan dinners that still happen on the bad days?
Plan four, not seven, and make one of them deliberately trivial. The plans that fail are the ones with no slack, because a single late evening cascades into ordering food for the rest of the week.
The rear derailleur skips on the third gear when I push hard.
Cable tension first: a quarter turn on the barrel adjuster while pedalling usually finds it. If it only skips under load and shifts cleanly otherwise, suspect a worn cassette paired with a new chain, which no amount of adjustment fixes.
Does this still hold if I am working alone?
It gets easier, not harder. A fair share of the difficulty is coordination, and that disappears. What remains is remembering your own decisions, which is what writing them down is for.