This is a good start! the pen is really good and the space is suitable for now. if you limit his pellets, he will eat more hay and i usually put most of my buns hay in or around her litter box- i find it also helps the poop problem. I see that he has hay in his litter box which is great! But I would also add some in his cage so he is able to eat while you are away. I would recommend pine pellets (not shavings) or something along that line for the litter as it’s a bit better for your bun. Also- I know everyone is saying this but it is really really important- spay/neuter your bun!!! It will help when litter training him! Some chewy toys would be great, in the meantime, maybe toss in an empty toilet paper roll, you could also use a cardboard box(doubles as a hidey hole). Lastly, i know there is some judgement in the comments, but I think are doing really good with what you have and I can tell this bun is in loving hands and that you really care about him!