1st timer need advice on buying used

Thanks downtheroad. Yes, the QX56 is basically just a Nissan Titan/Aramda with a bit more luxury. The payload is about 15-16K can't remember, tongue weight is about 870-890, again can't remember exactly. Id like to stay in the 5-7K range, and yes, will be adding 600-1K lbs of "stuff".
Thanks again for the reply. Im in the process of sifting through various threads on here now...