appears to be just aluminum, no mention of zinc
About 13 inches.
1 1/16 Socket fits.
A 1 and 1/16" socket is required, and maybe a longer handled ratchet.
The core is a steel wire that will not be consumed
I don't see why not, although you should be able to bend it at the last section to get it into the hole.
Rheem recommends that the anode rod should be removed from the water heater's tank annually for inspection and replaced when more than 6” of core wire is exposed at either end of the rod.
Yes, just trim it at one of the narrow points. These help to make the water heater last much longer