Happy to provide any info or ideas or just be here to bounce things off... I love campaigns, it was the fact that Fuzzywuzzieswiflasers was talking about setting up a VSF campaign that stopped me being a lurker here and got me to take the plunge and start posting.
I suspect that you'll have to write your own 'campaign system' but really that's not very hard. The system for the Atlantis campaign is so simple that I could explain the basics in about 2 minutes. But though there has been a mass battle of the type you're talking about, that was difficult to fit into the main flow, as were the aeronef battles that were fought. It's best for one-on-one land battles, it seems. So I wouldn't advise the Atlantis campaign system for your battles.
Objectives are a great way of keeping track of campaigns though - physical objective markers (captives, ammo, food or fuel dumps etc) on the field can be a very handy way of 'keeping score' (in Game 1, the Japanese take 3 objectives, the Parrotmen take 2, the Prussians and the British 1 each, the French and the Americans none - the relative success of the different armies is easy to see in that case); or objectives can be less literal (the Prussians get 5 campaign points for completing their objective, occupying the Automaton Factory; the French also gain 5 campaign points for capturing General Piddling-Ninny, the British commander; the Americans gain 3 campaign points for destroying more than half, but not all, of the Prussian Klankentruppen, etc).
These kind of sytems make the 'win or lose accounting' easier - and armies can complete their objectives even if they suffer massive casualties, or converesly can emerge relatively unscathed from the battle but fail to complete their objective.
Anyway, soem quick and unstructured thoughts on objectives and rewards... hope some of that helps you out anyway. Honestly, I'll happily discuss ideas about how to organise campaigns until the Morlocks come home, PM or post questions and I'll eagerly waffle on for ages.