Welcome

The Xterras are pretty reliable even up around 150k. I would check on the timing belt that is sopposed to be replaced at 105k miles. If it breaks, you may bust up the valves and need a couple grand in repairs. You also want to check on the exhaust manifolds as they were known to crack, and the rear seal as some have had it leak. Those are the most expensive items that may be possible.

5 of the 6 plugs are easy, the sixth will usually take a little while to get to as it's tucked down by the firewall where you can't see. You'll find instructions if you search.

If those items are all fine, you should have a great vehicle.