Everyone who is a moderator on the Stack Exchange network is completely voluntary and there is no pay. You may see employees with moderation privileges, but being an employee is not the same as being a community moderator.

https://meta.stackexchange.com/questions/169205/do-moderators-earn-a-salary

For question two, Stack Exchange is also built on a system of community moderation using a reputation system the more reps you earn the more privileges you can gain. This means that the users who are doing those task you mentioned don't have to be moderators. The regular users can also do moderation task as well. Therefore taking some of the load off the moderation team.

A second case for question two is that a site may not have as much activity which can allow the moderators to watch over more easier.