what is the "Private key" needed to access the REVS asset in future? The 12 word seed in our ICO account? or something else?
You don't need the private key unless you are holding BTCD in your own wallet. In that case, you need the private key for each BTCD address that has funds in it. You can get this from using dumpprivkey command from the Console in the BitcoinDark QT wallet.
if my BTCD are on the ICO platform, I automatically get REVS asset, without needing a private key?