Question about attacking in Clan Wars?

I just finished watching videos from the 4 youtubers that went to Finland to work on the Clan Wars feature. Needless to say, I am extremely excited for this feature to come out. Great work Supercell. The fact that it will be separate from multiplayer mode is great. Loot will be generated, defenders won't lose anything, it all just points to being fantastic.

The question I have about attacking is how the armies work. Is it a sandbox type of mode where we don't lose our army compositions? or do we get to choose a troop composition during preparation week to use, in which we don't have to spend our resources? Main point being, I just want to know if we need to put our own resources into the attacks, in which we would lose the troops once the battle is complete.

Any and all comments are welcome. Please let me know if you have any information or simple opinions on the matter. I look forward to taking on your respective clans http://forum.supercell.net/images/icons/icon6.png