To get natural freehand straight lines set the background to 0% opacity, press 'C' to turn on the precise cursor and then follow the checkers lines or squares to get straight and 45 degree lines (see the 'crayons' below).
The squares can also be used to get multiple lines that are the same length (see the 'equals' sign below).
I guess the trick is to play around with the settings.
Since there are lots of different results possible, I may have to start cataloging settings for effects I like and try to settle on just a few at first.
These you show are useful.
I'm still messing around with anything that gives the look of an oil painting. Mostly palette knife, brush and tube.