First of all, thank you both for the feedback.
Romeo, that helped a lot it starting to get a good dilution, I will try to do that. I'm building the A380 with the Emirates decals on it, hopefully it won't get that bad.
@Skodadriver, thanks a lot. The compressor is a cheap one, I though that for starters, that would be enough, but I agree with you. If I find myself getting better at this, I may consider buying a better compressor and airbrush. Regarding the thinner, I'm using the one from Revell (I will use it for the Humbrol paints as well, I believe it's ok). Priming is also something I will do, I bought the Mr Surfacer 1000 (I believe that's the name) from Mr. Hobby, and also bought the Mr. Hobby thinner for it, even though it wasn't necessary probably. I will give it a test with an old Airfix model I have here, just to test the dilutions, it seems it really is the most difficult part of all this process 🤣