The bumps are called fallout - shit in the air
Picking with your finger nail is about the worst way, try the clay you will be AMAZED! Shouldn't take more than 10-20min for clay bar step.
For the rust . . .clay will only remove the upper surface, more of a temp fix. If you maintain your paint then clay bar 1-4 times a year will prevent the rust from showing. To fully remove "rail dust" an acid wash is needed.
Easy way to remove fall out(ferrous oxide) - Clay bar
2nd choice - Wet sand & heavy polish
3rd choice(best) Acid neutralizer/alkaline neutralizer/normal wash