hey
i sorta work 4 a custom spraypainting garage n ull need to sand the bar with 800 grade sand paper till theres no shine AT ALL!
if u dont then theres a good chance the paint will flake off later on.
u wont need to prime it so long as theres no major dints or scratches (depends how nice u want it to look)
if u get it 2 that stage i think ull b suprised how cheap places will paint a bar thats all ready prepared.
remember paint fades over time so just looking the colour code up on the net might not do, u might hav 2 adjust the colour 2 match. thats tricky.
good luck with it