A few tidbits that are relevant to this broad topic:

- You can recruit level 4 agents with the right buildings: +2 for province speciality buildings; +2 for top tier of agent building. However, you don't get the two retinue you would normally get by levelling up generically.

- Monks (and I guess missionaries) seem the easiest to level: they can demoralise armies at zero cost in gold and success rates are decent (my only agent loss so far came from this though, so it is not entirely without risk). Ninjas can level fast too by sabotaging buildings or armies, albeit at some monetary cost. Metsuke seem hardest to level - the only active mission you can spam seems to be bribe and that is costly.

- The game says monks are vulnerable to ninjas/geishas; ninjas to metsuke and metsuke to monks. However, the RPS aspect does not seem strict. High level ninjas can have good assassination chances against all lower level agents. High level monks/missionaries are very powerful against lower level agents of the opposite religion.

Quote Originally Posted by Xploring
For question 3, religious agents have better odds if the target is of the same religion.
Are you sure about this? They have an action "character conversion" that in the encyclopedia (and logic) says works on characters of the opposite faith. I'd assumed it was like incitement to revolt - you get better odds if the target is of a different religion. I will look out for how to fares.