Depends on how far you want to deviate from normal play, you can technically recruit all the boss monsters on an initial playthrough if you're willing to play in a really weird way. The answer also kinda varies on if you want your final playthrough cycle to be Perfect or if you just want to see everything. No chapter has more than 3 endings.

Cycle 1 ( weird grind in Chapter 1 to unlock Demon Lord title, collect all recruitable boss monsters except Forest Lord Cub (get the skill instead because this will save redundancy later ), this requires getting a lot of Bad Endings for chapters (so you may as well collect all the "Worst" Ends ) -> Cycle 2 Demon Overlord La Pucelle Route (Good End ) -> Cycle 3 (you now don't lose story characters on a new cycle ) Get the 2nd Worst Ends where available, get the Forest Lord Cub this time -> Cycle 4/5/6 Back to Overlord Priere Mode and do the Bad / Normal 1/ Normal 2 Ends -> Cycle 7 -> Get the Best Ends for each Chapter

You can do the post game concent on any Main Story Cycle (but since story characters stick after Cycle 3 I'd recommend then, otherwise there's not a time when you have full grind access and all characters ) , NG+ stuff unlocks in the Main Story Mode at any point on Cycle 3+ , you'd usually want to leave it to later but since you're breaking the game something fierce on Cycle 1 it doesn't matter.

As a side note the game would be slightly easier if you did the Special Ends where available on Cycle 1 (the Unique Items you get are really good ) and did the Worst Ends for those chapters on Cycle 7 but that leaves you with an "incomplete" final cycle, so that might require 1 more loop depending on how you feel about such things.