It looks to be around 10 to 15 yrs old. It is hard to say for sure. I can only quese at best. I thought it was a hermans , but after second look I think now maybe Iberan greek/ testedeo grecae ibrea (forgive any missplelling).
You can use alfalfa hay or the pellets. I don't like the pellets because if the soil them and then eat them you are asking for problems. I use cypress mulch that does not contain cedar. Everyone has their choice. Check out the tortoies web sight. As far as making an out door pen, that would be the best choice. I would recommend the largest space you can make. Use cender blocks for the walls. You will want to dig down aleast 1 ft and start there with the block wall. That will prevent Harry Hoodieny from exscaping again. Dig out the top soil and put in 2 or 3 inches of gravel followed by a 50/50 sand and soil mix. Build the walls at least 2ft higher then inside ground leval. Also put a board or something over the corners on top. Some tort can climb walls. Give him lots of hiding places and shade. You will need to preditore proff it as well. Racoon, possums, and foxes would love to help themself to a free meal.
I commend your willingness to try to get it back to the original owner. However you may want to consider and be prepared for other issues. How did it exscape for them in the first place? Did the just dump and unwanted/uncared for tortoies? If it did exscape, can they fix the issue that allowed it to exscape, or will it happen again? The next time it may not be lucky and find it's way to your door! Now having said all that I know I would be going out of my mind if one of my beloved torts got out, and I would realy want it back!
Do you have other reptiles, or is this your first experince with the Herp world?