Real Time OS support for NIOS-II

You can put as many NIOS CPUs as you want, as long as you have enough logic cells in the FPGA to support it.

AFAIK there isn't any operating system that supports multiple CPUs today on the Nios II platform. I'm pretty sure that eCos doesn't, and even for Lunix I think that the Nios lacks some features to do SMP properly.

The eCos operating system supports several network interfaces (2 by default I think, but you can patch it to support more) but you need to check the driver. Some drivers are very badly written and use glabal variables instead of the structures provided by the operating system, and this means they won't work well with multiple interfaces.