1. - Usually this is spelled out quite clearly when the associate is hired. For example it might be "On weekends you will lead the high school ministry, one weekday evening you will lead our Teen Challenge, you will supervise the discipleship of the Teen Challenge small group leaders, and you'll do pastoral care for all teens and parents of teens." or "On weekends you will be in charge of infant care and the K-8 ministry, including all Sunday School curriculum, and the training and discipleship of Sunday School teachers. During the week you will lead the discipleship group for our staff of intern pastors, and supervise them as they do pastoral care." Another expectation might be that one 24-hour period each week they carry the "Bat Phone" and handle all emergency calls. Other things - Attend the daily staff prayer meeting, attend the weekly pastor's staff meeting.
2. - During the week he gets day out of the office, and the expectations is that his ministry cell phone will be OFF. Home phone numbers/private cell phone numbers for everyone on staff will be known by the senior ministry team, but will be given out to NO ONE. This is important, because ministry really isn't a 9-5 job. It's really easy for it to "creep" and take over every day, every waking moment. Even the "one week day plus Saturday" isn't necessarily the norm anymore, because many ministries have active Saturday night meetings.
3. - Wow, that's really broad.
"Misconduct" is a euphemism. It usually means one of two things - Women or money. For associate pastors, who usually aren't given access to money, it usually means women. The two guidelines here are "make no provision for the flesh" and "avoid even the appearance of evil."
Next is gossip/grumbling/back biting. If you speak against a member of the senior staff, even if it's "justified," even if it's "in confidence," then you might find you have just talked your way our of a job.
As for who makes the decision, that's a matter for how your church is governed. Some churches are run by a board and the pastor is sort of a "hired senior administrator." Some churches are run by the pastor.