I think you have a few issues going on.
First a good OBDII scanner for a reasonable price is a Foxwell.
I have a 520 Pro. I think that model has been upgraded to the 530 Pro.
It does everything the Durametric does for around $175.00 and you can load multiple manufactures programs on it.
Second:
I am guessing with this so take that into account.
If you changed the plugs and now your smelling raw gas and some plugs seem like they are not firing. My guess is that you have crossed up your plug wires.
Make sure you have the coils on the correct plugs or Cylinders.
Third:
The weird screeching noise!!! Could be that the Power steering pump has not picked up the fluid yet so the pump is dry and whining.
Again Just guessing here!!
Keep us posted let us know the outcome.