Potions are not limited in quantity or transferable, but everything else is. Essence Orbs work just like Alpha/Beta packs, you just specify an "edition" of 2 for those. Skins are also limited, transferable tokens, and there are new custom_json operations for transferring those.
The new cards will be part of the existing promo set, so they shouldn't require any changes on your end to work with.
I'll have a pow-wow with @asgarth when he's available to go over all of this.
I have a question on the potions Matt. If the potions give better drop rates to a pack, then does that mean there will be more cards available of the higher levels (ie more legends and more epics?)??? Or is there going to be the same amount of legends and epics, but when people with the potions pull better odds it reduces the odds of the other "normal" $2 pack buyers? It would seem that it has to be either one of the two, but maybe I don't understand it. Looking forward to learning more soon!