Knowledge of the domain and general experience with similar domains helps. My horse sense about what's likely to change has improved with time. As far as #6, yo

Knowledge of the domain and general experience with similar domains helps. My horse sense about what's likely to change has improved with time. As far as #6, you don't want to outright limit change because the future surprises, but use a YAGNI-ish view of unlikely changes to keep the system simpler. In other words, you don't make it hard to change, you just don't spend complexity on things unlikely to change. You only spend abstraction-related complexity on things likely to change.