honestly this depends entirely on what brush i'm using and the canvas size i'm working with (or it's dpi)
Like i work in medibang so for thinner brushes especially ones that taper at the end of a stroke like marker, pen or gpen then i'll keep it to 3 or 4 unless i'm going for a specific varied line style then i can go up to maybe 5 or down to 2 but no more or it can start to look off
For my chunkier brushes like the custom splatoon one i edited or default chunky pencil or pixel brushes then i definitely stay a bit larger with the size set no lower than 3 or 4 otherwise the brush spacing makes things look funky but no higher than 6 for some for essentially the same reason, otherwise i just duplicate the line art layer and flatten it a few times till i get the desired line density
the smallest i've ever gone is definitely 1 or 2 but that's only ever been with the pixel brush i use sometimes (the default and a custom brush i got from somewhere)
for reference the canvas sizes i work with range from 600 * 800px to 940 * 1080 all the way up to 1280 * 1650 but it depends on what i intend on drawing (i.e. it's a sketch/doodle canvas, a wallpaper, icons, comic pages, or different illustrations)