Answer:
#1 this is a primary source! a primary source is a material that has been recorded first hand by those who experienced it.
#2 this is a Rock Edict in the Mauryan Empire, they could only made at the order of the emperor
#3 Asoka was victorious, yet at a great cost of human lives from his side and the Khalinga. because of this bloodshed, he thought of this as a useless conflict and he felt guilty and remorse.
#4 the text says "When an unconquered country is conquered, slaughter, death, and deportation of people [are taking place] there. Thus arose His Sacred Majesty's Remorse for..." and this proves it!
#5 Yes I do think this is a credible source. this along with many other stone edicts are there to support this. moreover, this was done by Ashoka himself.
Explanation: