It’s great that you saved this bunny
As for tips, have a browse on the different sections here and you will learn A LOT. But it’s definitely a learning curve as Bam said and chances are you’ll make mistakes, but we all do
Give Thumper as much time out of his crate as possible and make sure he has plenty of grass hay (timothy, orchard, oat are the ones I know of but there are more) They should have leafy greens every day too such as romaine lettuce, rocket, watercress, kale, parsley, dill, carrot tops, chicory etc. Fruits and carrot are very high in sugar so should be given in moderation, I. E. As a treat
To keep him entertained, baby toys are great. Stacking cups, plastic bowling pins, baby keys, giant legos are all enjoyed by my two lops. Willow toys that they can chew are usually appreciated too.
Not sure what your cage set up is like, could you post a photo? If you’re using bedding all over, most of us here reccomend not to do that because it can make litter training more difficult. So just use litter substrate in the litter tray and keep the rest bare or with a fleece blanket if you absolutely must have something on the bottom.
Would love to see Thumper if you can post photos for us 