Hi
To work out PSI:
12 PSI = .83 bar
15 PSI = 1.03 bar
Viscosity is a term for liquid that basically means how ‘thick’ it is. High Viscosity means it is very thick, say like honey, where a low Viscosity means thin, like milk or water…
You can spray some acrylics like Tamiya paints in one layer but not others. AK, MIG or Vallejo really need to be sprayed in light layers or the paint will not be smooth -it will bead, look like orange peel or other ‘bad things’!
Even with Tamiya paints the best results are done with thin layers. This lets you add more or less paint in some areas, which gives a subtle variation in the depth of colour. It also makes sure you do not get a thick build up around details.
With thin paint you can pre-shade (make corners and areas around fittings, etc, a darker shade) by spraying a thin coat of a dark colour (or light colour) in certain areas first, then spraying your base colour in thin layers over that so the pre-shade colour makes your base colour darker or lighter in some areas.
Pre-shading demonstration:
Painting the base colour over the pre-shade
If you are new to using acrylics, I would stick with Tamiya or Gunze. They are the most forgiving paints for novice users. Once you have mastered using them, with low pressure, thin coats, etc, then you can look at others.
HOWEVER, no matter what type of [paint you use, the clear top coat should always be thin layers to avoid white build up. Even Dullcoat from Testors can react badly if too thick - I know that from experience.