Is it a sin to apply for a job that would require you to work on a Sunday, without good reason?
As long as you’re still able to make it to mass I wouldn’t think so. Around here there’s so many options for Sunday mass (Saturday at 4, Sunday at 9, 11, 1, 7:30, etc) I can’t really ever get away with using the excuse of having a shift for not making it to mass. It all really depends on what you believe though. Not very many years ago everything was closed on Sundays in what can only be called an effort to keep the sabbath. In our ever more secular world this is no longer the case most places.
Yes, although the Catechism makes exceptions for sports, restaurants, and social necessities.
You can attend the sunset mass on Saturday if your work does not permit you to go for Sunday mass. That fulfils Sunday obligation.