A rather huge encounter

[Nihb]

One suggestion I've read is to regroup some of the units into swarms, limiting the amount of dices to roll. Pool the HP, use the same initiative, modify the unit's attacks so it's area of effect-based or increase the amount of actions.

That would mean the soldiers would be able to attack more easily, as would the bandits, and leave the leaders as their own units, but helps the team's wizard, and may weaken the rogue's abilities.

Using the same initiative for every unit may help, but it will still be a hell to organize on the battlemat.

Edit:
One thing that makes the decision so difficult in this battle is the fact that the bandits and PCs are lv2, and the soldiers are lv3 to 5 (mostly 3). The players (and the bandit leader, the only lv3 on the "good" side) know the odds, and want to put everything on their side. A head-to-head battle would be disastrous.

Thus, they chose the terrain, a trail in the mountains where they can block retreat routes and control the high ground, hiding behind rocks and trees.

I must deal with stealth, perception and strategy. As much as I like BRC's idea, I can't seem to see it work in this context. I know it's a tricky situation, and I want my players to feel their strategies made a difference.