I just visited Giverny myself and loved it. But I'm not sure it'll be open in mid-April next year.

Thanks again to all who chimed in! This is a lot to think about.

Just as a follow-up, my sister and I are booked to do this trip in April. I left it up to her and we are only going to the Netherlands, staying in Amsterdam near the Museumplein. I think with all the things in Amsterdam to see for both her art appetite and the usual suspects such as the Anne Frank house and Resistance Museum, etc, plus daytrips to the Hague, Arnhem (K-M museum) and the Keukenhof, Zaans Schans and perhaps Cologne (for something different), she made made a good decision with only 7 full days in the city.

I will of course post a full trip report when we get back! Thank you all!!