After playing for a while, I suddenly realized that to achieve the best income for an econ planet, it's best to keep the population low. Do this after you have Galactic Stock Market tech because the Stock Market act as a Econ booster, a Morale booster, and a Influence booster. If you do the math or run it trial by error, you will find that a class 12 planet with 2-3 farms and all Stockmarket (plus the usual 2 factories) will produce significantly more credits and higher moral than >3 farms and entertainment buildings and whatnots. After finding the optimal point, I found the best ratio was to have 23,000 population for mid size (class 10-12) planets. At that point, each stock market will generate more income on that population than any additional 1 farm + 2 entertainment ratio. And over all, it will still keep the population quite happy and create a HUGE influence world to boot! I also happened to end up with a class 35 planet(50% evil PQ bonus!! Only time ever compiled with doubling PG from a natural event! Lucky). After some math and trial by error, I found the optimal income producing setting is 9 farms (59B pop), 4 extreme stadiums (wut i have at the point), 15 stock markets, and 4 factories. It generate 553 BC's per week. Probably more if I haven't build my econ capital elsewhere before this planet got big. I get less income from this planet if I build more farms and thus more stadiums. And I get less income if I build more Stock Market and less farms/stadiums.
My class 8 planets generate on average 220 BC's per week at tax rate of 40% and 90-100% morale with a setting of 2 farms (17B pop), 8 Stock Markets, and 2 factories. If I up the tax to 50%, I get average 270BC's per week with 80-90% moral!
Oh, i did take the mega econ race bonus and hold 1 econ resource.
