Diet questions and entertainment

I just got a young bunny (15ish weeks) he's malnourished and dehydrated. He has unlimited hay, but he just isn't that interested in eating it. He absolutely devours any greens and pellets he put his eyes on, do you have any tips on how to help him gain weight and encourage eating hay?

Also he runs free when someone is home to keep an eye on him, so he doesn't eat all of my furniture. do you guys have some DIY toys suggestions to entertain and engage him.