Hi Al Farouk,
1. All the Fab Process related files like Design Rule Document, GDSII Layer description files, Verification(DRC, LVS, ANTENNA) files, Technology Files(tool specific like cadence or synopsys or magma), Layout Parasitic Extraction files.
2. For the Backend Design you need the libraries(either from fab or from library vendor like Artisan, Nurlogic, VST......). The steps in the Backend Design are FloorPlanning, Placement, Clock Tree Synthesis, Routing.
3. MPW is usually done for prototyping. Here as others said the reticle cost, wafer cost are shared by different customers. Some fabs call this as Silicon Shuttle. I believe almost all fabs has calender for MPWs.
4. The final layout database in GDSII format is the final output to fab with DRC/ANTENNA report(optional) along with Tapeout request form which contains your process details(like single poly four metal 1P4M....., GDSII size/window, passivation opening.....) and the IP details used for the design.
-Sudhir