BEGIN TERENOS RAMBLING!
Okay I think the most interesting idea being bantered about is Colonials At War. Yes, you will need a map of the Old World, and a map of the New World. -Everywhere- in the old world must be assigned as a place, have an npc/pc government and so on and be kind of genre savvy (building up your forces should be met with building up their forces, where it can be afforded)
Everyone would start with their section of the Old World, and a new world colony should cost a certain amount. Most if not all places should be able to afford this, if they're able to get the ships together (Maybe some sort of variable cost, You just assign a fleet to it and hope they succeed, with larger fleets having more possibilities for success?). This way its possible for everyone to get a colony happening, but it might not be for everyone. Some people may want to play the game of backstabbing and powermongering in the Old World for a time. Nothing wrong with that.
Now that said, borrow heavily from whats been done before. From other Countries at War game you can steal/co-opt that wonderful effectiveness table. Or break it down to be simpler. Every unit/ship has base stats, which can be modified by research. Just some ideas of what you're looking at, unit-type wise, Infantry, Cavalry, Archers, Cannons, Light Naval, Heavy Naval, (Im proly missing some things here, but I must ramble ONWARDS). Of course everyones Pikemen will be the same, at base, but my pikemen might be better because I researched them
Anywho. Colonial Management rambling time. Now, initially having a colony should have large amounts of bonuses (otherwise who would want one?). Morale, Monetary, access to new resource types. For simplicity it should come down to money. Because you're taxing trade, and the people themselves. You'd be able to spend money, to increase the amount of money the colony is bringing in (at a better Return on Investment than in the Old World). This is another area research could come in handy to close potential holes. You roll a colony on the new world, at whatever location, and find X resource, why your people have never heard of this before, we must study how to improve yields of it so we may make millions at trade.
If you go that route, you have a research line for every type of research (Which isnt hard, Agricultural, or Industrial resources, and appropriate lines of research).
*stops rambling*
Also include variable victory goals from the start. Own the biggest new world colony without it forming its own country, crush X Old World Capitals, and become an empire. So on and so on.
But yeah, Colonials at war? I'll be the dude playing a New World native faction, and trying to keep you all off my land.