hey, yes you can mention about shielding.
For your first question,Think about it like this, as the number of electron shells increase as you go down in the group this means that the hold of nucleus on the electron in the outermost shell decreases. right? Therefore it will be easier to remove that electron in the outermost shell. That is what they mean here by less energy. The thing you misunderstood is that nucleus is removing its own electron, it is talking about the energy required by the neighbouring atom to remove that electron. I hope it helps.