I guess there is not much difference between using mapped drive and network shares. It is up to you how you prefer to see the paths in the Path column (an whether you want to be able to filter based on the network share name, or the mapped drive letter). I's say that there is no need to create mapped drives only for X1, but is you want to use them anyway, then go ahead.
No, it won't - in order to show a preview, X1 needs to be able to access the file.