A lot of confusion in 1st law of thermodynamics
I'm glad that you have got good concepts but the problem is you're unable to connect the discontinuous dots. See, in order to answer your first two questions I would like to bring attention towards the difference of microscopic energy (energy possesed by the molecules present inside the system) and macroscopic energy (energy you get to see in the system). As a example, a cup of coffee is placed over ground all will say it has zero K.E and 0 P.E. But the molecules present inside the system posses both K.E and P.E. You are right with the fact that change in internal energy for ideal gas means change in K.E but the change in K.E means, difference between the total K.E(summation of K.E of every molecules present in the system) of the sytem before and after the action. In case of non ideal gas, here both P.E and K.E both will contribute.
In case of sublimation of Na, here solid is changing to gas you can't neglect volume change also you have to keep it in mind that change in enthalpy is equal to change in internal energy if the PV-work is zero and the process is isobaric.