ADVICE NEEDED FOR AIRBRUSH NEWBIE

[jimdaloo]

Can anyone help me as I am just about to airbrush my first bodyshell.
I have a few questions that I need answering.
I have bought some opaques from Jon at RCS and they seem very thick do they need thinning and if so what do you use tried water and all it did was bead on the plastic was this because of ambient temp as I sprayed in cold garage or paint was to thin or is water not the right stuff
What needle should I use (I have bought the metal bodied Aztek ) so I have a vast array .
What Psi should I spray at and should you spray in the warm rather than a cold garage.
Any answers would be really appreciated.