Hi Ivan. Just a quick suggestion re your airbrush practice. One inexpensive and painless way to practice is to use ordinary ink, or perhaps those cheap, semi-liquid watercolour paints - the type in bold colours, in large plastic bottles, designed for young children to use. Mix these to a suitable viscosity for airbrushing, the mixing/thinning drills being part of the practice. Use these in your airbrush, spraying onto drawing paper, copier paper or whatever. You're not looking to create a work of art, the purpose of the exercise is to familiarise yourself with the airbrush, it's controls, action and limitations. This will enable you to practice 'triggering'; the art of controling the flow of air/paint by variations in the trigger pressure/position. Also, vary the distance from the nozzle to the paper, to gain experience in how the distance, pressure, trigger etc effect the spray pattern, weight of colour and so on.
Obviously, some people learn, or adapt, faster than others, but you'll be surprised how quickly you will be able to achieve consistent results, from broad, light, misting, to thin, hard lines.
Once you're happy with this practice, transfer to using your chosen type of paint (i.e., acrylic, enamel etc), and again experiment with the thinning ratios, and repeat the practice, eventually substituting the paper for a piece of plastic. An old model, or a cheap kit assembled in basic form only, is ideal for this. I actually keep a 'hack' model just for this purpose.
One of the most important factors, once you're happy with the above practicing, is to learn how to hold and control the 'brush. It should be held comfortably, with flexibility in the wrist, but spraying should be done at a consistent angle to the work. That is, don't twist your wrist to one side to 'hit' an area, this will diffuse the paint pattern, causing blotches, and/or patches that are heavier/lighter than their surroundings. Always keep the spray pattern at a 90 degree angle to the surface being sprayed, commencing the spray before reching the 'target', and following through, stopping the spray off the 'target'.
Think of it as if you were spraying a full-sized car - the only difference is that everything is scaled down, from the subject, to the tool, to the mist of paint. This, of course, means that any imperfections will be more noticeable.
And always remember, two or more light, or thin coats, are better than one heavy coat. Never go over an un-dried coat, as this will cause lumps, sags, runs, and a very uneven finish, as well as other anomalies such as 'orange peel', 'fish eye' and 'pebbeling', terms that you will, no doubt, eventually come to know!
I hope this helps a bit.
Terry.