You might enjoy Bismarck: A Life by Jonathan Steinberg. It goes into great detail about questions like this.
As berman647 says below, Bismarck was above all a pragmatist. He famously said "Politics is the art of the possible."
Enacting these "liberal" policies had three goals: strengthening the German economy, undercutting the Social Democratic Party and the power of the socialist movement, and the reduction of emigration of young German men to the US.
He managed to create welfare programs that were acceptable to the conservatives and helped secure German workers but that took the wind out of the sails of the socialists. The way the programs were implemented, with government enacting its policies via industry mechanisms, is a result of this.
Bismarck "switched sides" several times in his long career, and would again when his anti-socialist efforts fell apart and he attempted to ally with the Catholic Centre Party (who he had previously spent years attempting to crush) which ultimately led to his dismissal by Kaiser Wilhelm II.
The best way to think of Bismark is realpolitik. Above all else, Bismark followed the idea that political reality and requirements, not dreams, should govern political actions. His institution of "liberal policies" during his reign all fed into the idea that a strong German Reich required such policies being enacted. He was NOT a liberal (in the modern sense) - but had a distinctly amoralistic approach to governance. He saw Imperialism as a waste of effort and kept his worldview local (to Europe). It's also worth noting that his boss, Kaiser Wilhelm II attempted to undue or leave unresolved many of Bismark's reforms (instituting the Morocco crisis, German imperial endeavor, diplomatic gaffes, etc.) and helped set the stage for WWI.
There is an interesting documentary about Bismarck from 1940, German Biography of Otto von Bismarck (1940). This one has English subtitles in case you do not speak German.
Just make sure you remember who it was made under in 1940!
How much of Bismarck's reforms were Bismarck's, and how much came about due to the work of the Reichstag?
And how did that Reichstag work, anyway?