As season 3 which is 26 episodes long will cover the Coalition Invasion Arc which is 100 chapters long, I bet that season 4 and season 5 will cover the following arcs :
Season 4 : 81 chapters
1) Kyou Kai's Revenge Arc : 9 chapters
2) Conspiracy in the Court Arc : 13 chapters
3) Fire Dragons of Wei Arc : 23 chapters
4) State of Ai Arc : 36 chapters
Season 5 : 58 chapters+
1) Koku You Campaign Arc : 48 chapters
2) Bureaucrats Job Arc : 10 chapters
3) Western Zhao Invasion Arc Part 1 : ? chapters