There are usually multiple strategies to successfully completing a scenario; these can be discussed on the scenario's discussion page or written down in an existing or additional section of this article.
All of the base rides have extremely inflated Nausea stats than is normal, so replace all the rides (except the Wild West show, since it has a rating of 0). As for the Avenger, you have two options: Complete the ride or demolish it. Either one works, but if you choose to complete the ride, replace the brakes towards the end with block brakes so you can run two trains at once. Then hire four mechanics and assign two to the adventure side of the park and two to the western side and the rides should get up and running fairly quickly. Then hire 4-6 janitors. Trust me this isn't enough janitors to clean the entire park, but you don't need to do that anyway. Instead, just spend time deleting paths, one square at a time and replacing them with a new square. You can even change the type of path if you want. This will have you set for the VIP all the way through tycoon level. After that just spend time building rides and you should be good. Also, build the second coaster on the western side of the park because if one side has more coasters than the other the side with fewer coasters tends to lose a lot of popularity.