A344: My understanding is that you only have to pay once when you first use your Destructive Blast, even when using blast shapes with a duration (such as the talents you listed, as well as Energy Sphere or Energy Wall).
A345: Neither! There are some similar thematics, but ultimately you're inflicting them with energy rather than a disease. While a creature hit with Energetic Affliction might be riddled with boils of acid or literally burning rashes, it's just a particularly nasty expression of destructive magic. It works equally well on undead, constructs, or even objects. A wall isn't going to catch a disease, but it sure can catch fire.