You can legally fish it if you are in the river, not from the banks. East of Delsea Dr, the north side is mostly owned by TNC (there are a few private properties), and the south side is mostly owned by private landowners (there are a few TNC properties as well). There is a gas motor restriction upstream of the railroad bridge. Meaning, nothing but electric or human power is allowed above the bridge.
Yes, the river has everything the Maurice has. Bass (stripers, largemouth), perch, catfish, etc... Fish it like you would the lower Menantico.
Yep, no fishing in the sand washes. There are some largemouth in there, but nothing to write home about. So it's not worth your time anyway.
FYI, outside of the core Pine Barrens or the upper Delaware Bay marshes, the middle of the Manumuskin Preserve is one of the few places in NJ where you can go and not hear any road traffic.