I'd probably agree with Jorrs - the amount of time and money you will spend on cutting back a shit job and doing it again will drive you nuts, especially if it's your first time spraying a car...and yeah it's REALLY hard to match faded colours unless you are a professional so you are much better off spraying the whole thing. I wouldn't attempt to match colours, hell I recently did my bumper and I can tell that the colour is miles off the rest of the car even though it's the factory mix. (by miles I mean it's just a different tint, and probably a polish or two away from being as smooth-a-finish as factory)
Having said that, it is possible to do a very good job yourself but you had best do your research about how to get the paint down evenly and you need to spend a bit of time practising spraying stuff (just get some sheet metal or scraps) to get used to how to operate a spray gun -> there's lots to learn, I've been DIY spraying stuff for ages and I think I've only just recently got enough experience to possibly tackle doing a whole car.
At least you are choosing a flat colour, metallics are a little trickier (but not impossible).
Last piece of advice, don't rush! And concentrate 100% - professionals may look pretty relaxed about it, but they focus 100% on what they are doing.