Got my first boxes of Epic Scale Waterloo the other day. I worked out a pretty good system using both the Citadel Contrasts and some of the new Army Painter Speedpaints.
On the Youtube channel "Miniature Realms" the fellow who runs it, Stewart, utilizes the Zenithal technique, with an airbrush pass of black followed by an airbrush pass of white.
Link to his British infantry painting tutorial:
YouTube link
For my first two sprues, I did a similar thing, but I experimented with black rattle can primer and then did a manual drybrush of white over that.
The airbrush is by far the better way to go. The variant I tried leaves the models too dark in some recesses for the Contrasts to properly show up, and the black spray primer had a bit of texture to it. Might have been a temperature or nozzle thing, but the drybrush over it gave the models kind of a rough finish. In the end they came out fine, not a game breaker. But like I said, airbrush is a much better way to go for Zenithal.
In any event, Contrast paints are without a doubt the best way to go with the Epic Scale system. I attempted to paint several sprues of the Civil War last year with traditional model paints and almost lost my mind. It just takes forever. The Contrasts speed up the process many times over, and you give you a one-pass shading and base coating.
So go with either a Zenithal, or a straight light colored spray primer like off-white or white.
The one big advantage of the Zenithal is that since a good deal of both armies have white straps and belts, you can let the Zenithal itself be the final finish for those areas, saving a HUGE amount of time. It's already shaded. Also worked for the white cross-lacing on the front of the British jackets.
At this small of a scale, painting the primary jacket colors of red and blue really amounts to painting mostly just the sleeves, with very small dot-size ares of jacket on the back.
The Contrasts and Speedpaints worked excellent for the uniforms, shakos, muskets, and flesh areas.
For the knapsacks, rather than laboriously paint the white straps for every single one, I did a gray and brown Contrast over them first, then did a white drybrush over them and the blankets to make the straps stand out. Would have taken twenty times longer to manually paint the straps!
The only areas where I used regular paints was the silver on the bayonets and musket barrels, and white for some of the cuffs and to touch up some of the white straps and belts.
The artillery each had only two Contrast colors, yellow for the brass barrels, and then a green and bluish gray respectively for the gun carriages.
I got one sprue done for each army, taking about two afternoons for each sprue.
At this scale you can get away with quite a bit in terms of not painting in every single detail. I shaded a lot of the equipment with a simple light gray Contrast to give it some shading. The most important thing, especially for the French is to make sure you do give distinctive colors to cuffs, shako pompoms, shoulders, etc. Those colors really help the scale pop from tabletop height.
All in all a pretty efficient way to get the armies painted up reasonably quickly.