I have just joined the community and have been reading the documentation for a day or two, but do not yet have permission to log onto a machine due to the University not having completed the paperwork. But reading the documentation a number of questions occur to me about the relationship between Linux and the RCCE and the LUTs on the cores.
Linux on the cores .. full access to files ... I think so ... I've created files, written to them, read from them. If you come across limitations, let us know.
RCCE users operate with one RCCE process per core, and that is its intended operation. Having said that, I don't see anything inside RCCE that would prevent you from running more than one RCCE process per core. It's a change to the usage model, but may be worth trying out.
The addresses in the LUTs are physical addresses.