[question] unit balance and city income

I'm making a custom map based on a fictional world. I'm curious if any of the more experienced mapmakers have experience on how to balance units (range, HP, att/def, etc), to ensure a given unit isn't too powerful or weak.

Additionally, I've already learned how to determine reinforcements in line with the base map but I'm curious as to how income is calculated for each city, so that I can mirror it in my map with my fictional cities.

Thanks in advance