Hi Laura,
Your approach sounds reasonable, I'm not sure why Eclipse is giving you errors. I created a test workspace and attempted what you described and I found that I could not automatically import some classes, here is a screenshot when I attempted the "fix project setup" option from right-clicking on the highlighted code:
If I click OK, it configures the libraries of my custom project to include the rapidwright-api-lib-2020.2.6.jar as shown below:
This might be the issue you are experiencing. I suppose Eclipse doesn't export the jar files setup in RapidWright, so you probably have to add them directly so they are on your CLASSPATH. Hope that helps.
Chris