I'd go over the whole lot with course, and then fine paper in the sander.....The new paint needs a decent surface to key into, but it needs to be fairly matt, without any deep scratches that would show through the new paint finish.......and don't make the same mistake as a "professional " paint sprayer that used to be on here made.....Make sure you thoroughly degrease the surfaces before painting, or the new paint will just crinkle up.......especially around the filler hole on the tank...... And, as RantMachine says, you're best off removing any badges, etc rather than trying to mask round them......