I'm glad you like the direction of our game, but to address your concerns, I'm not quite sure what exact sort of bookkeeping you have in mind, as all gaming systems have some of it. In 3.5 you need to know the hit points your NPCs have lost, whereas in 'Bastards, you'd be much better served knowing what body parts of your NPCs are and aren't covered in armor. Both of these are bookkeeping of a different kind. It's the players that need to decide which form of bookkeeping is more fun for them and choose their system accordingly.
So, such general inquiry is hard to respond to, but keeping accounting at a minimum has been a high priority design goal.
As for your concern of 4 PCs facing 6 NPCs in melee combat... I've yet to see that happen, period. One of those ten people is bound to pull out a pistol or a bow and then most these fights will break apart instantaneously as the characters scramble for cover.

In short, most fights of that scale become skirmishes by necessity. And if a character or two have their ranged weapons out in advance, these massive every PC vs every NPC melee brawls won't even occur as there are much more effective tactics to employ.