I recently read that Pickett's Charge, one portion of the Battle of Gettysburg in the American Civil War, had 10,000+ soldiers on side and 6000+ soldiers on the other side. While Battle of Gettysburg is of a different setting and is an extreme example, it does make me think of the general scope of army sizes in a fantasy setting.

What would you consider to be an appropriate size for an army in a major battle in a fantasy setting? When playing a "regular" game of Warhammer (Fantasy or Age of Sigmar) what does the matches represent at minimum for:
1) actual great battle between armies?
2) just a portion of a major battle between smaller divisions of the armies?
3) skirmishes between expeditionary forces, town defense, brigands, etc.?

For me, I think at least ~1000 soldiers on each side to represent a major battle. ~500 soldiers minimum on each side to represent a portion of a major between divisions within an army. Skirmishes there are no real minimum. So for gaming purposes I think a major battle between armies would have to be played out in multiple games (for example representing the left division, center division, right division, etc).