Re: op amp biasing
It depends very much on the type of op-amp, some have self biassing built in, some don't.
In general though, if you have DC negative feedback and sufficient current in the feedback path to supply the input stages, the output will adopt the same voltage as the non-inverting input. I am ignoring the effects of fixed drops or offsets in the feedback loop which you may have to take into account.
So with negative feedback, if you use a potential divider to set the voltage of the non-inverting (+) pin to half supply voltage, the output will also be at that voltage. Ignoring the tiny effects of input bias currents, that means you use two resistors with the same value in the potential divider and connect it between supply and ground.
Brian.