1) Needle size (I use 0.35 iirc), but perhaps too large for painting figures and tiny stuff. I also have a 0.5 neelde airbrush, but I really never use it. Maybe I could start using it for gloss coats, unsure.
2) Quality. Well, a cheap airbrush might work, but if the needle isn't always centered, you might end up with clogging in my experience. And then you might end up buying more than one cheap airbrush,
3) I prefer a self centereing nozzle (Iwata HP-CS Eclipse), one large nozzle that is easier to clean because it isn't super tiny nor something you have to screw off. Also expensive if/when you replace it.
4) Never rub the tip of a fragile nozzle, not even with the skin of your fingers (that was a lot of money out the window one day, it happened unintentionlally)
5) Forget about siphon feed airbrush (bottom fed), instead get one with gravity fed paint with a paint cup on top.
6) Size of paintcup on top, ought to be, not too small, or you can't airbrush much stuff without refilling, and maybe not too large, if you are airbrushing smaller scale models and not t-shirts or very large models.
7) I am only familiar with an aircompressor with a tank. Faller/SilAir some older model.
8) You will need the typical airbrush "pot", for both cleaning (spraying into), and it also functions as a stand.
9) You will need a spray booth with proper ventilation, or risk contaminating your room and/or iimpacting your health negatively imho.
10) I only use acrylic paint (Vallejo) which is much less obnoxious/noxious/toxic than enamel paint and I am happy with it.
11) Vallejo primer paint, ought to be always sifted into a mixing jar to remove small flakes of dried paint, or risk major clogging issues. I have now, zero, clogging issues doing it this way when airbrushing Vallejo primer paint.
I think the biggest issue here, is aquiring a spray booth that vents outside an open window, via a 1m hose or somesuch. Hopefully you won't have neighbours that will complain about that kind of activity next to them.
A typical airbrush is 'dual action'. I.e press down for full air, and pull back for adjusting flow/amount of paint. Some have an additional function, like adjusting the air on the airbrush but this can also be done with a valve on the end of the airbrush, connected to the air hose from the air compressor.
You might want to, at some point, want a paint limiter. This is usually a rotating knob at the end of the airbrush handle, which sets a limit to how far back you can pull the knob when airbrushing, thus limiting the flow of paint. Sometimes it is good to know that you don't risk putting on too much paint on accident or being overly eager. For my Iwata airbrush, I had to buy such a paint limiter as an accesory.
Always have a spare needle and a spare nozzle around, just for that one day, you do something stupid when handling your airbrush.
22. September, 13:46