Regarding the consensus for filenaming, how are we suppose to adapt our search process ?
There's no need to change the search process. The search should work as before, consensus only affects indexing.
Do we need to add naming consensus in the process of file download ?
This is a neat question! Are you referring to the filename that the client provides for saving the file locally, which is automatically shared? In this case, simply assume that the client first performs the search and learns filename-metahash binding from it. Then, the client uses the learned name for saving the file locally.
This is a simplification, which avoids that the client runs consensus for the chosen filename, consensus which would fail anyway if the client's chosen name is different from the one of the peer sharing the file.
What about having the same metafile having two different filename, is it allow ?
No, that's not allowed. Consensus should reject the second filename mapping to an existing metafile. Please check out this post.
Does this address your concerns?