Nice uncle. 🙂
Wiping is better, but one simpler thing you could do is just to create a new admin account for yourself, log into that new account, and then delete your uncle's old account. That will delete all his private stuff in his account.
Which model? If no SSD, put one in.
How much memory?
Which version of OS X? The latest is 10.10 Yosemite. It's a nice OS, but the only problem is if you install a 3rd party SSD, you won't get TRIM support. Not a deal killer, but not ideal either. TRIM support works fine on 10.9 Mavericks though.