xibeijan, for your question:
Transfering XCP cost no fee in XCP. Same for assets.
But you have to have BTC on the same privkey as it will cost you 0.0001 BTC for each transfer.
The data will be save in the OP_RETURN function on bitcoind v0.9, allowing 80 byte if I'm correct.

The  --fee_provided=.001 or  --fee_required=.001 might be in XCP.  edit: answered it's in BTC.
From what I understand, they are optional.
But honestly I don't know about them.
Not digged that yet.