Probably OEM sensor, given where you got it installed. Factory o2 sensor will have a toyota or denso part number on it. It will also not have any splices in the wire.

The front and rear o2 sensors do different things. The one in front before the cat regulates the mixture to whatever is programmed in the ECU for current rpm/load/throttle. The one in the rear, behind the cat, simply indicates whether the cat is working so it can light the check engine light if it's not.

I don't know what the o2 voltage readings should be. I have not observed them while my truck was running: PCMSCAN periodically reads all the values you specify, and if you ask it to keep track of more things then the period becomes longer, reducing the number of data points in your log for a given time. So, I only check the ones I'm interested in.