1) Your understanding is correct1) I don't think the SMOD Nissan Radiator class action affected the Armada - but I would double check. It did go to 2010. So long as it doesn't have it when you buy it - easy fix - either just bypass the radiator cooler or replace the rad.
My understanding is virtually all VK56 exhaust manifolds are disposed to crack. There not a big deal to fix, but are integrated with the catalytic converter so there very expensive - is my understanding. Never owned one - so you might want to do some more research on that part.
There otherwise very reliable, if not hard on fuel - is my understanding.
2) A lot of other competitors manifolds are also prone to cracking. Virtually all V8s designed in that timeframe have thinner manifolds as a way to heat up the engine /cat combo quicker for Emissions:
https://www.tundrasolutions.com/threads/cracked-exhaust-manifold.77228/
https://www.benzworld.org/threads/exhaust-manifold-cracked-twice.1640318/
https://forum.ih8mud.com/threads/ex...y-potential-damage-how-urgent-to-fix.1285045/
3) As reliable as the sun it takes an extrenal event to damage or wear them like inhaling catalytic converter particles from a broken cat with an ignored SES emisisons light. Even neglecting oilchanges unless extreme is well tolerated.
Every single Nissan V8, I ever owned (I owned 5 since the 90s, not counting my current VK56VD that is near new) made it past 180,000 miles at zero oil use, perfect compression.
If the toyota fanboy serial owners were honest and they had as many as I have they would not be able to make that same statement.
Excessive Oil consumptions tells me there is imperfect compression and not all the advertised HP will be prsent in an aged motor.
There are even entire threads on oil usage on the Tundra forums and Lexus forums.
There are no such oil use threads on the Nissan forums, because none are needed:

https://www.tundras.com/threads/oil...thing is perfect and,and watch the oil level.
https://www.clublexus.com/forums/ls-4th-gen-2007-2017/978305-burning-oil.html