Dusty Desert/Scenario Guide
Start off by building a few flat rides to bring in some money. You shouldn't invest in either of the five coasters yet until you have some money coming in. Set research to Thrill and Gentle rides, plus shops and stalls at maximum funding. This will attract some guests and give your park some money to scrape by. Plan out your pathways by connecting queues and pathways to the Inverted Roller Coaster and the Steel Twister Roller Coaster (two of the B&M trio); mainly due to the Inverted Roller Coaster crossing over the paths and it allows you to build flat rides in between the roller coasters.
Once you're ready, build the Steel Twister Roller Coaster. As long as you don't go overboard on G-Forces, the ride should easily meet the excitement requirement. A great way to give the ride a small footprint and little impact on other rides is by making it go above and below ground and have it intersect itself, this'll also help the excitement rating. Also, a launched lift hill will help you conserving space. Let the ride run its course and hire a personal mechanic (give him assigned space directly at the exit) if the train is going faster than 30 mph (48 kmh) into the station (that's the magic number for crashes on all roller coasters). The ride should attract a lot of guests and give you more money - just don't forget to increase admission to 5$ or more.
The Inverted Roller Coaster will need some boosts in excitement because they are easy to build too intense. Have the ride cross over some paths and itself to build excitement, also decorate the station and add tunnels. Avoid building large loops and keep the G-Forces as low as possible (below 4 Vertical and 2.5 Lateral at least) and you should be golden. You can choose launched start to conserve room, but this will allows only one train, so this would kind of waste the long station. Hire a personal mechanic for the ride because most likely, the ride is going faster than 30 mph and might crash in the future.
Tick roller coasters in your research because you'll most likely be out of research for thrill and gentle rides soon, expand with the latter two a bit to make some more money and attract more guests. You can build a normal coaster if you want to make some more money at this point, it'll only help you in the long run, just avoid the ones that cost more than $3,000.
Now, expand your park and connect with the Wooden Roller Coaster and the Flying Roller Coaster. Finish the Wooden Twister Roller Coaster first, since it's cheaper to build. Give the ride some twists and hills, a helix, and have it cross over and under itself and other rides before connecting the whole thing to the last two helices. You might not need a personal mechanic for this coaster because the last two helices burn off some speed and the ride shouldn't be going faster than 30 into the helices.
The Flying Roller Coaster can be tough to build, but as long as you avoid high Gs and too many inversions, you should easily have it hit 7, even 8.
Consider building the Vertical Roller Coaster last, since it's way off the path and also expensive to build. Give the ride a vertical brake element for the first drop, which builds excitement, and have it drop into the ground (possible without any landscaping if you have the track in the right spot). Have the ride transfer above and below ground to build more excitement. When you plan to finish the ride, have the track end at height 6 and use a vertical brake element to stop the ride, this prevents deaths in case of the infamous Station Brake Failure. This ride easily has a 6 excitement rating with just a vertical drop, so with the added stuff, it should easily be 7.5.
You don't have to connect the last coaster in order to complete the objective, it just has to be tested to have enough excitement and be opened, then you're done. If one of your coasters is not exciting enough, add tracked rides like Car Rides and Go Karts to twist around the track, decorate the station, and add tunnels.
This works with all the other coaster building challenges in the game.