is there a method that allows me to define how many systems a flow must have?
Sometimes, when formatting a flow, for example, you notice that the last page only has a system or two and so the page may be 50% “empty”, while I need it to be completely “full”.
Being able to define the number of systems per flow would allow to define and completely “fill” even the last page.
No. You can put a Note Spacing Change anywhere you like, though, and it’ll then automatically reset to the values in Layout Options > Note Spacing at the start of the next flow. I find this quicker and more elegant than adding various system breaks manually, excepting the situations where systems really need to reflect phrasing.