For parts, the easiest way to set the systems into pages is: set an appropriate value for the gap between systems in Layout Options > Vertical Spacing. I usually reduce the value to about 7 spaces.
For multi-flow works, I turn on Flow Headings and let flows run across pages. Then I just set a few Frame Breaks where I need to, for good page turns and to get whole movements on a spread. If you want to force more systems on a page than the default, use Make Into Frame (or apply two Frame Breaks, and click on “Wait for next Frame Break” in the properties pane of the first one.)
If the music is simple, you can set bars per system and systems per page in Layout Options.
I can create a set of beautiful instrumental parts in minutes with Dorico. The trick, I think is not to do too much: let Dorico do it.