Clothes or other soft stuff (cheap fleece blankies I’d recommend) on the floor will protect his feet: as LPT says, he can hurt his feet on the chicken-wire and develop a difficult-to-treat condition called sore hocks. Buns don’t have padded feet like many other small pets, so they need a soft floor. You would have to shake out the blankies once a day or so, because he will poop on them.
Try to get him to pee on something that you can put in the litter-box, or soak up some pee with a piece of old newspaper so he realizes that’s where pee should go. If he will at least pee in the box and put most of his poop there it’s great, the poop isn’t really super-yucky since it’s dry. Intact boys can be hard to train but some will take to it. My bunny Bam was over a year when I got him and he got the hang of going in a box in a few weeks or so and was fine with it for a year (then he had a hormonal burst, but that’s a whole other story!) Buns often like to much on f ex hay when they go so hay in the box or near it is very good.
Revolution (selamectin) is the best anti-parasitic for a bun, as LPT says. Some vets will give Ivermectin instead. Fipronil (frontline) is deadly. Both selamectin and ivermectin will get rid of intestinal parasites as well iof he has any (it seems like he’s been pretty neglected in his old home), so that’s a plus.
Other than that, food is key to bunny health. Lots of good hay, a small amount of good quality pellets + a slow introduction of leafy greens one by one over a couple of weeks will be great for him.
Thank you for takin him in. We’d love to hear more about him!