Oh, i've had a PS4 since it came out in 2013, it was just the original PS4 model. The pro has super sampling tech and whatnot due to the better hardware, for sure RDR2 will look better there.
As for PC, there's no word out on a PC version yet. GTAV PC version came out about a year after the console release. Wouldn't surprise me if the same happened here.
RDR2 will deffo have a MP component, but I'm sure it will be something akin to GTAV's MP mode, where it's a completely separate experience from the SP mode. I didn't like GTA's MP mode much, but I think it did really well, wouldn't surprise me if they got more revenue out of that mode than purely from the game sales.