Volunteer Experience

Your out of work activities carry a lot of weight as it adds colors to your profile. If your career is not as interesting (hunting boars or researching mushrooms for a living), your extra activities can mean life and death to your application. It's how you can add values to the school community. Your activities do not have to be volunteering though doing something for free sounds a bit cooler

1 It does not count as volunteering but you can list it on your app
2 You can list this too but they probably want to see you lead something rather than just participate or just help out (since you are applying to be future leaders)
3 You can use college volunteer exp but current exp count more and talk about college exp less and highlight only significant one because the longer the college exp looks, the more it looks like you haven't done anything since school. Which is also OK, if you work for high demanded job (100 hours + a week and no time to rest)

For your last question, it depends on the school you are applying to. If you are applying to top school you will be competing with kids who was number one gamer, number one shark hunter, number one chess master, etc. who have the same job and score as you. But if you are applying to top 30 - 50 you should be ok