Yes, very open hours.
No, 20 hours a week is the maximum for international students.
According to CIC website: - https://www.canada.ca/en/immigration-refugees-citizenship/services/study-canada/work/work-off-campus.html
International students cannot work more than 20 hours per week, but i have heard that yearly hours are checked when applying for Post Grad Work Permit. But you never know,right?
Its better to remain in safe side rather to be sorry.
This may be dependent on your work visa.
If you're manager thinks it's okay, then go for it. just tell them how many hours you're available for and they'd give you hours. if you want only 20 hours, tell them that or if you want 24 hours, also let them know... it's as simple as that really...
Its okay to work any amount of hours
I'm unsure, you may want to talk to your manager or maybe e-mail someone who deals with this stuff