You have plenty of time and land available to reach this huge goal, so start building, and don't stop too soon!
This is a take on the previous level "Evergreen Gardens", a huge botanical garden for you to turn into the country's best theme park experience. First, block off every path in the park that goes away from the entrance area, like you should have done in Evergreen gardens. You may want to take out the huge bridge in the front, as many people will complain about the vandalism and amount of guests in the area later on, but it is a nice place to put stalls and such.Put some flat rides and any track ride (Wooden Wild Mouse Coaster or Car Ride work the best) right next to the entrance, as well as the basic things, like toilets, info kiosks, and food and drinks. Once you have a good amount of people and a steady income, expand into the park. Place flat rides in the flat places, and take advantage of the hilly terrain, and get roller coasters that go underground, which will increase the excitement rating and have a small chance of becoming an indoor ride, a huge moneymaker at all times. You'll need 60% of the track underground for it to work. After a few coasters and a bunch of flat rides, you'll have enough money to be creative, and after that, go with whatever you'd like. This is easier than Fiasco Forest, Urban Park, and especially Harmonic Hills, so have fun, and keep using advertising campaigns to your advantage.