Don't be intimidated because this is the last scenario. Although not easy, this is not an extremely difficult park and the main difficulty is the setting of your terrain. This is one of the few scenarios in the game where guests can have a long walk to reach the rides. However, this shouldn't be a big problem as there is also a Chairlift. You might want to consider building roller coasters on top of the rock and smaller gentle and thrill rides in the desert. This can be quite a hard park, however, there is a lot that can be done here, and the guest goal is incredibly low for the time given.
Basically, this park has three areas for constructing: the top of the rock, the desert and inside the rock. You have 4 years to complete the scenario so you should really try to use these three areas. First, while the game is paused, you can fix the prices of the chairlift and set an entrance fee if you want to. Also set your research to thrill rides preferably. Keep in mind that after 4 years you'll have reasearched (if at maximum funding) all thrill, gentle rides and roller coasters available, besides some shops and stalls, so you don't have to worry too much about it. Unpause the game and start by removing or blocking the path on the top of the rock (just let the path that leads the chairlift exit, so the guests can walk up and down the rock only). Now, build some stalls and bathrooms in the park entrance and in the top of the rock.
Notice that your guests are quite poor, so if you choose to have a pay-per-ride park, keep in mind that several of your guests will leave after a while. If you have a pay-per-ride park, try to either reduce your prices after some time, keep your prices rather low from the beginning or then building continually.
You'll have to save some space in this park, because even though the rock and its interior might seem large, after 4 years it will most likely be completely filled up (and it's not that easy to work reasonably in the underground section). Just know that the large area on the top of the rock must be kept mainly (this is not a rule of thumb, but a good advice) for rides like roller coasters, water rides, and Go-Kart tracks, so build small gentle and thrill rides like Merry-Go-Rounds, Haunted Houses, Swinging Ships, and Scrambled Eggs on the desert. The inside of the rock can host a lot of roller coasters, so take advantage of this! Also, allow water rides to tunnel through the rock, as this will dramatically increase excitement ratings and save building space both above and below the rock. Build several, as water rides are popular in the desert and have high capacities, reducing the crowds on your paths.
Surely, in the end you'll probably not have got stuck with the idea of tracked rides on the top and underground, and flat rides on the desert. You can obviously have all kinds of rides everywhere, but that generic rule is a good way to start your layout.
Notice that you already start out with $10,000 and you can only borrow $5,000 more at the beginning. So, initially, money might become a problem, so be patient while building and have good sense. You shouldn't try to build a grand coaster right away because it will just make you be in the red. However, shuttle coasters are really a good option (again, it doesn't need to be a Shuttle Loop, for the sake of it). After some time you'll be able to increase your tracked rides' lenght and add bigger coasters to your park.
If you choose to build on the desert area as well, notice that, after a while, you'll reach the top right area and at this point, if you also developed your park on the top of the rock, guests will start complaining they're not finding a particular ride or, even worse, your mechanics won't be able to find a ride that is broken (so it's a good idea to consider setting patrol areas for your mechanics as well. Also, note that if you build paths from ride exits inside of the rock, mechanics might struggle to reach them). This can be fixed fairly easily if you build more pathways (underground) connecting the bottom to the top of the rock. Have in mind that, if you ever build through all around the bottom of the rock, you must also build at least four of these kind of pathways.
Four years is a lot of time for getting 900 guests, so you can reach the number until Year 2, but you need this time to complete the scenario in a good way. If you are short on guests by Year 4, make some marketing campaigns, although this shouldn't be a problem if you have enough rides and have continued building throughout the scenario.
At some point, you'll research the Vertical Roller Coaster, which you'll be able to build with a massive drop and make it your greatest coaster (as it can easily reach the 9.00's in the Excitement Rating).
Assuming this is your last park in the game, you may want to try the following: In October of Year 4, build a Shuttle Loop, but don't open it. Change the launch speed from 40 to 60 mph. When you reach October 30th, click the amber (test) light on the ride. If done right, it will crash right as the scenario is completed, producing a firework-like show. Congratulations on beating the original game!