1. Could be. Could also be from the same people that said Tamiya & Gunze paint are the same. And just because the same manufacturer makes them doesn't make them the same. BMW used to produce a sub-compact econobox, doesn't mean is was a 3 series BMW.
2. Because there is so much less travel on the air part of the switch, control is very tricky. Takes a much finer touch to regulate airflow.
3. Matching paint to plastic is very difficult. It's possible, but not easily so. Most plastic is slightly translucet, giving a depth to the color that paint can't match.
4. Should be, just watch how thin your paints are and keep your air pressure on the lower side.
5. Potentually. Without a reglator you're stuck spraying at whatever pressure the compressor puts out, likely between 30 & 50 psi. This is very high pressure for painting. The highrer pressure can lead to paint drying before it hits plastic leaving you with a sandpaper like texture. See if you can find a decent regulator, it makes all the difference in the world.