the difference between 5.3 and 7.1 lbs is 1.8 lbs. Is that something that you would notice though? If it is you could simply get a backpack that holds your laptop. Brentahaven has many such
backpacks. That would make the extra load unnoticiable.
As for heat, there is a bit. You do not want to wear shorts, and if possible having a table to put it on would be best so it can get proper ventalation. Personally I do not mind it though I've only used one, never owned one.
I can't say about the noise of the power adapter.