The LIGO collaboration seems to have pushed out a whole pile of papers with arxiv numbers sequential to the announcement, which are cited in the discovery paper. You might enjoy Properties of the binary black hole merger GW150914 and Tests of general relativity with GW150914.
If I recall correctly the spin of one precursor black hole is known with modest precision, while the spin of the other is completely unconstrained. The ellipticity of the orbiting pair had long been circularized away --- don't forget that the LIGO signal only captured the last eight or so orbits before coalescence.
I expect that any information about the charge of the holes is lost in the uncertainty on the mass estimates.
The accretion disks would have been transparent to the gravitational wave more or less like the rest of the universe was: essentially all of the mass density is at the black holes. However if and when we get simultaneous information about a gravitational wave event and a visible- or gamma- or radio-light transient, we can expect to say something about the surrounding environment. There were searches for optical and neutrino transients coincident with GW150914, but none were identified; however in looking for the no-optical-transient paper I found a cautious association with a gamma-ray burst.