I hope your angle grinder uses sanding discs, a hard grinding wheel will damage the metal.
You can probably get them cleaned up enough with angle grinder sanding and hand sanding.
You could also use paint stripper and then some hand sanding to remove all the paint, media blasting would be best.
Krylon spray paints would work for the black paint & would also work if they have the correct body color for your car.
Rattle can painting can give good results but takes many coats as the paint is highly reduced and its easy to get runs if your not careful.