Although you will get a huge excess, it is strongly advisable not to immediately spend massive amounts of it. Bear in mind inflation will increase. And a stronger economy means higher wages - wages which you will have to pay your civil service if you don't want them being very annoyed.
Go to industry, make sure u dont have any plastics industry, pause game around 8 am,subsidize plastics with 100000000 (or how ever many zeros fit in the bracket), unpause for 3 hours, pause it again, change the subsidy to 1, fastforward like a week, u should have like 400 billion, depends on how many unemployed people u have, ur inflation will rise by like 300% a year, that can be dealt with by increasing taxes and vat to 50%, in another year or so, inflation will be back to normal, then just lower the taxes and vat, of course if u have oil to sell, inflation will drop faster.
I'm playin as Venezuela, i have an excess of a TRILLION dollars, though i did it with oil alone, not using the trick above, but inflation will happen with oil too,
Also a good way to get 3 star army, is to buy on the BLACK MARKET, ONE UNIT of tank, missile launcher, nuclear sub, chopper, fighter plane, then just use the unit trainer option to increase their numbers, DO NOT BUY AIRCRAFT CARRIERS, the unit option in the trainer doesnt multiply the ship, it multiplies the aircraft on board, u'll just waste 8 billion, they are too easy to sink, also imo ships are useless as well.
Edit, one more thing, when u increase tax and vat, DONT increase salaries, try to make it trough the riots, if u havent transformed a country into a dictatorship, i cant guarantee you will stay in power, it's always good to be "friendly" with the military.
Also, use "green" energy as much as u can, imo nuclear energy isnt worth the price\energy output ratio, offshore wind and solar is wut powers all my countries.
I completely defeated China with only cruisers, destroying all of their coastal cities, nuclear reactors, power generation, etc.
Mind you, that did kind of crash the global economy. But swings and roundabouts.
I'm all about the Air Force, soon as i get my money, i build like 20 air bases, use the trainer and put like 1000 planes in each base and city, i went to war with USA, i took out all their nuclear plants and the rest of their power production, leveled cities, military installations, in ONE MASSIVE air raid, had easily like 100 groups of fighters, 1000 in each.
Playing as Venezuela, it's 2018, conquered Cuba, Panama, and a few neighbors in S.America, murdered USA, took out S.Arabia's oil production when i defended Israel, installed a "friendly" gov. in Mexico and in Netherlands (dont ask, lol)
But b\c of the unemployment i cant really conquer anymore nations, unemployment 5%, 45M people, yearly budget 600B, 7 trillion GDP, inflation 0.2, i have VAT and Taxes at 43%, and i cant lower them cuz inflation will start rising again, cant really cut spending cuz i dont wanna compromise on health&safety&education, although i have permanent excess of trillion dollars (doesnt seem to go down no matter how much i waste), maybe cuz im pumping 60 billion barrels of oil a year, LOL.
I figured i might play as my home nation of Finland, then annex a few small oil producing countries half way across the world, might be interesting.
I tried it with belgium and the netherlands and it worked, then i tried it with germany and china and it didin't even though i invested in an industry they did not have, I also tried investing in "all activities" but the value seemt to clip over or something made like 1mil% one day the next -1mil