Part of the run-up to getting anything done with this project is finding appropriate rules for each gaming subset. There are a multitude of wargaming rules out there to pick from. Pick from, meaning that I am going to find a ruleset and most likely modify it to suit the specific needs of gaming in the Half Continent; I do not intend to write my own.
I think that the mass battles ruleset will be the easiest to start, as the system will be used for Imagi-nation battles at first. Caution must be used, however, as the system must be malleable enough to accept the alchemical and the fantastical additions that will be needed. I do find myself asking if I should use a fantasy system, such as Fantasy Rules! and modify it towards a more historical feel, or find a historical system and plug in some mods for scourges, lahzars, monsters, etc. The fantasy system will have the fantastical feel built right in, but the historical rules will have the proper framework for what I see to be the underlying structure of the battles I want to create... decisions, decisions. In either case, I am looking at having the battalion, roughly 300 to 500 troops strong, become the smallest independent unit on the mass-battle tabletop.
As for skirmish rules, I think that something in the Song of Blades & Heroes family will work - simple, fast, and detailed enough for bring the flavor of the myriad of different types of people and monsters out. The finding of suitable minis will be the key point for skirmish battles however.
Naval battles might be based on a suitably simple system for galley battles, or even (more likely) American Civil War ironclads, although the ships involved would dwarf anything found in history prior to 1875! More on that aspect later...