better part made mercie: mostly made of mercy

absent argument Of my revenge, thou present: try to get my revenge on someone who is absent when you are here

with Candle: diligently; perhaps alluding to "If she lose one piece [of silver]... light a candle... and seek diligently till she find it." (Luke 15:8)

turne: return 

More villaine thou: Duke Frederick, ironically, condemns himself

of such a nature: experienced in such things

Make an extent upon his house and Lands: extent meaning a) to value and/or b) seize, confiscate Orlando's land and property

turne him going: meaning send him (Orlando) packing