I tend to focus on minimum force necessary. Large armies are expensive and take too many mouse clicks though ironically, disbanding stuff takes even more. 2,000 decent troops with even a bump though, can basically run through any reasonable number of enemies in any mod I've played, so large armies are ungainly, expensive and micromanagement-intensive gestures.

And let's face it, even if they were necessary, I doubt I'd have the energy to go through with such a long battle.

In many of my games, my largest armies never see combat or in those rare instances I insist on playing Conquest, don't see combat until the end. Those are armies running 3-5 stacks whose purpose for much of the game is simply discouraging AI aggression so I can sit on a point lead.

Sometimes, I'll pile together large armies for auto-resolve. Those tend to also run 3-5 stacks or about 2500-4000.

Very occasionally, I run armies bigger than that. That absolute most number of troops I'd ever had to actually use was 4500 when I took some Spanish trash into Khazar to fight the horde. Armies at or above 5,000 are very rare for me. My record is under 9,000 Cumans.