It's not the fact that it's spray paint, it's all in how you apply it. The main thing would be to get automotive grade paint from paintscratch.com or something. Here's a few things I could think of:
-Two things to pearl: lay down pearl in several light coats to match the amount of depth of the pearl, and the distance at which you hold the can determines how light/dark the pearl is so you can match it. Same goes with clear coat. Spray a little farther away and it will lighten up due to more light being refracted from a slightly rougher inner structure of the paint.
-Do NOT blend side skirts into the door. No paint job is ever going to be 100% match, so I'd personally much rather have the line be between two body panels than right in the middle of the door. I had a fender replaced on my MR2 and the shop blended it into the door. Looked like crap. My pearl white audi had the fenders and hood resprayed at one point and they just sprayed the fender and hood and didn't "blend" it into the door and it looks so much better than the MR2 did.
I'm all for DIY. The people that are telling you not to do it are people that are afraid of doing it themselves and screwing it up. I say give it a try and report back to us.
Also, if you have plans to do more paint work in the future, you might just want to look at getting an inexpensive paint gun from Home Depot and getting pints of paint so you have extra down the road. When I painted the whole bottom side of my Audi it cost me like $40 for a Husky HVLP and about $200 in base, pearl, clear, and hardener. This was my first attempt in laying pearl. Ended up putting too much on, but was able to lighten it up by spraying the clear from farther away. Still have enough paint to spray a spoiler or something.
