Oil Temp:
The black goes to any common chassis ground. Any unpainted metal surface will do.
The red goes to constant power.
The orange probably goes to switched ignition power.
The green goes to the sensor.
If you tee off the oil pressure sender at the back of the block, you can fit the oil temp sensor in there with a 1/4" pipe thread joint.

Water temp:
I have no idea where you would place the sensor. I would assume somewhere where coolant flows...:thinking:

A/F ratio:
You want the primary O2 sensor. That is the one upstream of the catalytic element. The white wire will be sliced into and the green wire connected.

I think you are way over your head with this project. What is the need for all these virtually pointless gauges again?