About the idea of ditching A-H in favor for Russia: Since france was expected to be fought and hostile a couple of years down the road, antagonizing A-H would have put germany in russia´s pocket (sort of like ditching russia had later put germany into austria´s pocket, IRL). And since unified small germany (sans austria) was all bismarck aimed for, he had nothing he wanted to gain, by getting closer to russia and ditching austria. After the unification has been completed, maintaining the status quo was all bismarck´s germany wanted. Ditching any of the two eastern powers would have made that close to impossible, as this would a) give revanchist france an ally in germany´s back, and b) made an attempt by the remaining eastern friend to tip the balance between the three in his favor with german aid much more likely.
All this is actually demonstrated by the events after Bismarck´s retirement. After the treaty with russia expired, austria tried to improve its position on the balcans and russia promptly allied with france. Since austria was germany´s last ally, it had little choice but to back them (or so they thought). So especially in retrospective, Bismarck´s move not to crush ausria must seem a good one.
Speculative course of events, had Bismarck crushed and more or less dissolved austria: Totally dependant on russian friendship, the empire would be forced to let pan-slavism go rampant on the balcans, under constant russian threat to slip of into france´s hand, should the germans oppose. Wether germany would have been able to draw its head out of this noose in time by allying with maybe turkey and italy is an open question. Once russia would have everything they wanted, they´d still ally with france, to remove the german threat of revisioning their gains, possibly ending (back to particularism) the empire in the war to come.