# this man to be a pest

"this man to be a trouble maker" 

# all the Jews throughout the world

The word "all" here is probably an exaggeration used to strengthen their accusation against Paul. 

# He is a leader of the Nazarene sect

"He also leads the entire group whom people call the followers of the Nazarene"

# sect

This is a smaller group of people within a larger group group. Tertullus considers the Christians to be a small group within Judaism.