With a CW car any decent bodyshop should be able to provide you with a selection of spray out cards, once they find 1 that matches perfectly edge to edge you should be able to just paint the wing and fit.
Sometimes they may have to call up and get a service match if they are really struggling, but its an easy enough colour to match so shouldn't have any problems
They would need painting before fitting anyway to paint around the edges, there is no corrosion issue obviously, but there no way of painting the edges down the a pillar and such which you see when you open the door fi they are fitted before painting.
The perfect way is to prep, prime, paint, fit. Then prep again and blend out on the car, however with a solid colour there should be no reason to blend any painter should be able to achieve an edge to edge match on a solid colour, unless it is something very difficult
If its a metallic colour obviously it needs blending. You shouldnt need to blend the bonnet though as the angle difference will give you enough difference to not need to blend the bonnet, if they cant find a match good enough to only need to blend into the door then don't use the garage.
Bumpers don't tend to be blended either as there is always a very slight colour difference in metal to plastic so providing they can find a match there is no reason the match should be any worse than the original match from factory.
Look at Ford colour matches bumpers to wings from factory they are awful!