Are you dead set on Xterras too? Lots of SUVs fit your requirements for price and are similar in size and power and stuff. But I understand if you've decided Xterra for sure. If they are built anything like my Titan, I'm sure you'll love it.
Definitely get Carfaxes on whichever of your vehicles you're interested in. When I was looking for titans I narrowed it down to two, the one I got, and another that was about $3k cheaper. The one I got had service records of every scheduled maintenance done at Tim Dahle Nissan and was a 2 owner truck. The other one I didn't get had been in a front end collision (couldn't tell by looking at it) and didn't have very good maintenance records. During the test drives of each it definitely showed. My truck still shifts like it's brand new, the other had very soft shifts.