When I got my Navara, I didn't bring the revs above 1500rpm for the first 1000km (i.e changing up the gears as soon as possible without labouring the engine). Stayed below 2000rpm until 5000km. Had it serviced at 5k because a new engine will have more metal "powder/dust" in the oil than a new one while components seat in against each other. The metal in the oil can increase wear on engine (which is one of the reasons you normally need to change your oil).
I stayed below 2500rpm until after 10k, and only went above 3000 (which I rarely do anyway) after I'd 20,000km on the clock.
This might be excessively cautious, but it's a small inconvenience for the service you'll get back out of your Navara. Three years later I've 285,000km on the clock and it's still purring like a lion.
About towing:
I think it depends on the load you want to carry. If it's a fairly light load, I'd say there's no harm in it. If you want to tow a heavier load, I think it depends on how much throttle you're going to need while towing. If you can pull the load while keeping revs low and keep your foot light on the throttle (i.e not towing up steep hills, towing fast, accelerating hard, or driving into strong head-winds), I think it won't be a problem.
You'll have to judge the load for yourself. If it's not a necessity, I'd say it's better to be safe than sorry.
Hope this helps.