My personal opinion is that anyone who wants to do the FPW in 28mm needs to be a bit patient, because there isn't much else in plastic or metal that would be accurate and compatible with the new Perrys figures. I'm afraid the plastic French infantry are a few months down the line as yet, but I understand Michael has sculpted metal Chasseurs a Pied, which could be out quickly and so you'll have a first unit to hold off the Prussian hordes.
I agree you could do French Zouaves out of the Perrys ACW guys, so long as you don't mind the rifle being different and also the equipment. Off hand I don't think they are carrying much gear, so that might not be too problematic. And they are certainly in the right sort of "dashing forward" poses for proper zouaves!
Come to think of it, there are good, compatible figures available for the Prussians in the form of the North Star 1866 range, recently revamped and with many figures that will blend in to give variety and cover some current vacancies. These are characterful and accurate figures; some might be just a fraction on the bulky side, but would probably go alongside their plastic comrades.
I also agree with the good Baron's opinion of the forthcoming WA plastic Bavarians: just not up to scratch. If you are in a tearing hurry to have some Bavarians and aren't too picky about anatomy or details they might fill a gap. Incidentally, I could be wrong here but I don't know where the idea of some Bavarian infantry wearing caps "in the early days of the FPW" comes from. The Bavarians went to war exactly like Prussia and most of the other German states, ie wearing helmets, but also carrying their soft caps with them. These would be worn out of action or occasionally for a "packs down" charge, just like the Prussian infantry. The Bavarian cap was smarter than the Prussian version, having a peak and a chinstrap, but was just as much a softly constructed cloth garment that could be rolled or folded and shoved into the bread-bag.