The "d-n", n = a number from 0-10, specifies the d-electron count for a particular metal. Thus, "d0" implies that that the metal (in your case tungsten) has no d electrons. Knowing that you can determine the oxidation state of W.
I'm not so sure about your second question (I'd have to look into it). Hydrides exhibit a strong trans effect, so my first hunch would be that it causes a facial set of hydrides with elongated bonds (WHa3
with distance W-Ha
). The geometry of this would be c3v.