This scenario isn't difficult. The guest requirement is fairly low, and there is ample space to build plenty of roller coasters and other rides, even though the terrain isn't flat. Begin by switching research to stalls only and pushing the research investment to the max, you'll need a Drinks Stall soon. You can leave the Miniature Railroad, as its Excitement rating is good and the ride is popular, but if you are short on cash, then it is not absolutely a bad idea to scrap it. Consider adding a second station somewhere in the back of the park, in order to massively increase the ride's functionality & interest while also increasing the number of trains. Avoid however using long queues. A queue as long as two full trains is the maximum length you should build them : A longer queue will drain your waiting guest's happiness and basically ruin their day.
Then, do build a single roller coaster. Continue to expand outwards by adding new paths, path items, stalls, and staff. Four or five roller coasters should definitely be sufficient to bring in the needed number of guests to complete the scenario, and the time limit isn't restrictive. Be warned however: It rains a lot around here, so consider building lots of Indoor rides, or a roller coaster that is mostly (if not completely) underground. The Mine Train Roller Coaster is a good choice as it fits in perfectly to the scenario's theme. Remember to use the umbrella cheat for an easy situation improvement.
When you first start, the entry fee is $4, and you have a loan of $10,000 out of a possible $20,000, you can charge ride admission instead of entry fee. But if you build enough stalls and on-ride pictures everywhere you can, money shouldn't be a problem.