This scenario is one of the hardest Expert scenarios in RCT2. If you complete all of the Challenging scenarios, Rainbow Summit will be much easier for you. The fact that you can't build tall coasters is the main reason for that. Start easy by building stalls, gentle, and thrill rides available. Don't use the tracked rides at all in this scenario, because you will find yourself struggling to find space later on. Four years is a lot of time to build, but the question is how.