Okay, a lot of questions.
1st off, this site is a community forum that is dedicated to 343ind. and Halo and a few other topics. The engine being used for Halo 4 will be a mix of the existing engines of the previous games. I have a clear thread with links to definitive statements, interviews and videos here. There has yet to be any mention of destructible terrain, abilities or much else yet. They are keeping the secrets pretty well for now. Armor Abilities are a thing of the past if what Frank O'Conner and other members of the development team have said holds true. It is fair to assume there will be an enhanced forge that will offer more variety of objects, color, terrain and diverse forging environmental platforms, but again, they are not releasing a whole lot. You can listen here for yourself to Frank's own words or Kiki and Josh's words here in this fully descriptive and definitive interview by Gameinformer.