Spray Painting Scooters/bars/Parts:
Not a problem with the Bars since most are Steel but as mentioned rattle can paint isn't really that durable so they will Chip.... but you can paint them again whenever you want so not a big deal when they chip.
Grab some 150 grit sand paper and lightly sand the bars
Wipe off the dust.
Spray the bars- light coats so you don't get any drips.
FOLLOW the directions on the can for re-coat times.
Usually you have to re-coat within an hour or
wait 24 hrs before applying the next coat. This part makes a big difference.
Apply as many coats as you want but 3 should be the minimum.
I wouldn't bother with a clear coat- the bars are going to get beat up and it is just an added cost that has no real benefit. Just repaint when needed.
Decks: Since they are Aluminum, spray paint isn't really a good idea since the paint does not stick to the AL very good and will flake off, peel off, chip off quickly.
This doesn't mean Al can not be painted-but rattle can paint isn't the same stuff real painters use to paint aluminum so it usually just looks like crap.
You could Powder coat the deck but it is $$ and still isn't chip proof.
So... leave the deck alone and paint the Bars