Good morning!
1. No
2. The legal limit. I don't know about other parts of the world, but here all commercial operators have to monitor the exposure to cosmic radiation of their staff.
3. Yes. In the same way that I am concerned about all sources of cancer. It really is an evil and ugly disease that is best avoided.
Greetings, Max
NB: Forgive me for nitpicking (had another life before starting to fly...), but the most damaging particles with the highest energies - by several orders of magnitude - actually originate outside our galaxy, so "galactic radiation" is only a part of the problem!