You will be able to develop both characters as you wish (as with previous Divinity games, there is no strict class system). Not a lot about the equipment system has been revealed, but there should be a variety of armour (possibly robes, etc, if forum requests made after DD were taken to heart).

Nothing has been mentioned about copy protection for Original Sin (or Dragon Commander), but Lar has said in the forum and his blog that he is not a big fan of DRM (The pirate in me). Larian removed the DRM from Divine Divinity, Beyond Divinity and DKS (contractual restrictions prevented them from removing it from the original release of D2:ED), so now that they are self-publishing it is unlikely they would start going with more restrictive DRM.