Taking in a neglected Russian tortoise!

I've acquired a Russian tortoise who was severely neglected. I've been to his former house a couple times where he "free roams" but recently notice a lot of paint spilled in the room and I felt bad because he roams these floors- it's definitely not controlled at any temperature and I know he was definitely not regularly fed- or given really any water. When I went to where he was yesterday, I saw someone must have broken a glass, and swept it up as well as all the dust and other stuff that's swept from the floor was put in a pile which happened to be near a lamp, and the poor tortoise was laying in the pile of glass and I felt horrible. So he's come to live with me. I'm just looking for some general tips and advice. I've gotten him to eat some lettuce and raddicho, and some carrots. I've seen that they could drink water and walk around in it, so I filled a tin with a little water and placed him in it- he didn't drink it just wanted to crawl out. I've considered maybe I didn't use enough water and he couldn't see it?

I have a small cage set up right now but will be building something permanent for him this weekend but I'm not totally sure what to place at the bottom? I've read dirt/soil mixed with sand. My brothers recommended me use wood chips, so I'm not sure the best choice.

He seems pretty alert but I think his nails look a little... jagged- some are long, some are short and like the left sides shorter then the right. I've read that having a rock in the cage for him to scratch his nails on will help file them down?

It's a male Russian, and I'd have to guess he's around 9 years old.

Any tips would be great! Thanks!