Hi @April,
My solution to the arrows is using 2x geom_segment () . Probably there are nicer ways, but it works.
ggplot(mtcars, aes(x = hp, y = wt)) + geom_point() + stat_smooth() + geom_segment(aes(x = 100, y=5, xend=200, yend=5), lineend = 'square', linejoin = 'round', size = 2, arrow = arrow(length=unit(0.5, "cm" ))) + geom_segment(aes(x = 100, y=5, xend=50, yend=5), lineend = 'square', linejoin = 'round', size = 2, arrow = arrow(length=unit(0.5, "cm" )))
Hope this gets you going.
JW