Imperialism 2 is such an epic game!
I actually played around with a concept for building it onto Civ4, but then my Fallout mod picked up momentum again so I left it alone.
Yes M:C(Medieval Conquest) is the better choice for modding over tfan basic Col, although more complex. (you can do a lot more at just an xml level though, just means more yu have to learn to understand.)
Civ4 mods are not usually compatible with Col without modifying, so i would wave yourself away from that thinking.
The production part of Imp. should be transferable relatively easy, in spirit.
Especially if you use the same number of resources as M:C (Yields) I cannot off the top of my head count how many resources there are in Imp. but I don't think it is more than M:C
In the M:C code citizens can also 'consume' goods, so you can have the 3 level of citizen expert from Imp. Consuming their resources.
(At the moment hough I don't know if there is any consequence to not fulfilling the need, I think you just get gold from them... Night would know more.)
The trick with yields though would be replacing them 'cosmetically' rather than changing their code names as this requires modifying the .dll. Which is hard work starting out.
Other things from Imp. could also be done like 'Capital Production' where everything is done at home. You could make something like a capital building that is required for all manufacturing buildings, then everyone would have to work at this home base and all resources would have to be taken to the capital... something like that might work..
Expanding the map is doable as well, I did it once so it can't be that hard! I think it was just changing a couple numbers in a map size file somewhere, but my memory is fuzzy at the moment..
Here is all the stuff I did for World History Mod (I think). Feel free to scavenge. (some of the yield art might be useful.) It is based on a version of M:C that is two or three steps out of date with M:C though, so it is a bit out of love and was only ever the very first steps on the road. (I think it has the skeleton of a tech tree, extra yields(LOTS of extra yields) and possibly an expanded map size..) Still you are welcome to mine it all.
I also included some art files that I had gathered for use. Along with design files too.
The whole thing is quite large though.
World History Mod Content