Have been working as a support staff for a couple of Elite Author for more then a year now . Giving support for both WordPress and Jquery Plugins as well as WP Themes. To anwser your questions from my personal experience
1: It Usually depends on the amount of work that is required. Most authors usually pay hourly since some days the requests are high some days they are less .
2: Never signed one.
3: You should hire them for like a week on trial basis and pay them for there trial period. If they are good you will know instantly.
4: Usually the Support Staff makes sure that it is indeed a bug and not human error and then forwards it to the developer so that he can release updates or maintain a bug list and work on it.
All the Best,
I don’t consider replying to a 3 day old thread given its Monday today. And Its not Spamming. I am offering my services . Like many others here who don’t even have a legit account.