@Bad Pink Tink 2.0 thanks for the tag, Tink!
I am not a local to Efteling, but I have been a couple of times. It's an amazing park. There are some threads on here and tons of
youtube videos of non-Dutch speakers visiting Efteling, some branding it better than Disney ;-)
Efteling is a really nice blend of thrill rides and family friendly rides. It has one artistic style and has a lot of history. There is a small museum within the park.
Most rides are bilingual or have some signs outside in English, German and French. However, I know there is one ride where you want to look up the story in advance, because the Dutch pre show has a lot of story to it, and there is only one sign outside. This ride is called Villa Volta.
Best time of year to visit the Netherlands is in Spring, and if you go outside school holidays during the week you will find very low crowds in Efteling. If you need help to determine when there are school holidays, let me know.
On the other hand, it really is a park, so Efteling is gorgeous on a nice autumn day. Issue... we have a lot of rain in autumn.
I think at the moment there is only one ride with a fastpass reservation system.
If you have the time (as in more than one day), I know Americans love our Fairytale Forest, you want time to explore it. The Forest is what started Efteling in the 1950s, tableaus of fairytales in a park. And that has gotten more and more elaborated. You migt want to brush up your European fairytale knowledge (there are signs in English at each fairytale).
Download the app, it'll be a great help to look at waiting times and to get around. This park is huge. So also wear good shoes and be in good condition.
I have never used it, but Efteling should have wifi throughout the park.
Let me know if you have any questions!