First of all:
Welcome to the Forum.
Second hints and tips.
Each genre/scale/medium of the modelling hobbies has their own little difficulties and techniques that need to be mastered.
Gundam Robots tend to be snap-together and it is fairly hard not to get a good finish on one if one works slow and careful.
An Airbrush is a tool, same as a modelling knife, sandpaper, glue, etc you need to invest time, effort and frustration in order to learn to use it well.
First master the basics of modelling before you try the tougher and more advanced techniques.
Expensive and flashy tools don't provide the better results, those come from the modeller that uses those tools. And many Pro-Modeler hardly use any expensive or flashy tools.
Even the tips and techniques given and talked about here need practice, practice and more practice in order to be mstered.
Example:
Getting an airbrush and learning to spray an even finish is only part of the game, you also need to learn masking, mixing the paint, etc.
Best of luck in your ventures and study.