As for Naval combat, no, Fields of Blood does not address it. The closest it comes is mentioning moving troops by ship, and even that "assumes there are enough ships available". I like the naval combat rules in FFG's Seafarer's Handbook; the book is also just plain a good resource for adding some seagoing elements to any campaign (underwater combat rules, naval combat rules, feats, skills, equipment, aquatic races, and so on).
I think using MMS:WE to detail the lowest levels is a good approach. In that sense, MMS:WE makes a good companion volume to Empire or Fields of Blood. I think there is a little too much overlap (and inconsistency) with the BoSD for them to be used together, but it works well with the others.