Hi Pablo,
1) Yes, this is mostly training. However, in the selection process we do look for candidates who have certain abilities. See 2 and 3!
2) I can only speak for myself, but I don't find the job at all stressful. Sometimes it does get pressurised, but I love those days and I often get bored when it's quiet.
3) Being good at teamwork; remaining calm under pressure; being able to take on information from many different sources of information at once, prioritise them and quickly decide what to do with the information; good at solving problems; high situational and spatial awareness.