What is required of the servants of the Lord?
It is required that the servants of the Lord be Faithful.
The group specifically selected to be examples in 1 Corinthians 4:9-17?
The apostles of the Lord have been specifically selected to be examples of Christ and of his teachings.
Why is it not enough to simply know what is right? (Alma 39:11-12)
If we know what is right, but do things that are not inline with the teachings of the Lord, then others will see our example and not gain a testimony of the truths. We have to DO what is right so that others may come unto Christ. We must put off the natural man, who is an enemy to God.
What additional powers come to those who live what they know? (3 Nephi 8:1)
If we live what we know and bless others, our sins will be forgiven us, "cleansed every whit from his iniquity". The more good we do, the more good we want to do and the better we become. We become more valiant servants of the Lord.