Hi, and thank you for rescuing this bunny!
I can’t say what breed he is but his coloring is Japanese harlequin.
It is true that wire bottom cages can hurt the feet. There’s a difference between calluses and sore hocks, sore hocks is much worse and needs vet attention, calluses is just hardening of the foot soles. If it doesn’t progress further than to calluses, you’re good. You could use fleece in his cage instead of towels. Sometimes you can buy really cheap fleece blankets or pieces of fleece, and it’s a great material because it’s easy to wash and pretty safe to ingest little bits of. Buns often like to dig in fleece and build blanket mounds and drag pieces of fleece from one part of their area to another. That can be a nice activity for some buns.
Another activity that buns often like is chewing sticks or twigs of apple or willow. If you give him apple, make sure it’s from pesticide-free trees. Willow trees are rarely if ever treated with pesticides. Pet shops and online pet stores sell willow balls and apple stick, but it’s of course cheaper if you know someone that has trees and would be willing to give you a few twigs now and then. If you decide to buy chew toys for him, start with one or two, because he might not be interested. Because he’s an adult and has been used to a life of boredom, he might need a long time to understand how to use toys.
Buns also tend to like to destroy (“bunstruct”) cardboard boxes. An overturned cardboard box with two doorholes (they want two because that resembles a bunny burrow) works excellently as a hidey house and a home-improvement project. He shouldn’t eat the cardboard though. Ingesting a little bit is ok, but he mustn’t like devour it.
As for neutering, 3 years is not too old to be neutered. But if you have a single boy and he’s not displaying adverse behaviors such as pee spraying, he doesn’t have to be neutered. Neutering has few real health benefits for boys, we do it so they can have more freedom and to relieve stress in obsessively sexually interested males – and of course it must be done if the bun is to have a friend. Pee spraying and poop marking and other hormonal behaviors can crop up after quite some time though, for my Bam it took a whole year and he was an adult when I got him.