Research would be a good start, as that will help you determine size of map, colonies, yields, etc.
Figure out what time period you want to portray, and then dive right in. I haven't modded Col in a very long time, but for BTS I use Blue Marble and GEM maps as a base, and then cut it down from there to attain what I want.
I would recommend after doing your research, use WB to give you a basic idea of how things should be set up for your ideas, and then perhaps look at some of the modding tools here in order to fine tune things. Just my input, and good luck.
