Oil Cooler
#2
Its possible that it could cause a pressure drop or a restriction plus you are cooling the oil right before it gets superheated by the turbo. I dont really think that the engine will benefit from this. I have a scavenge pump on my turbo drain and the pump feeds the oil cooler then returns it to the pan. You could always do a sandwich adapter above the oil filter and run it to the cooler that way.
#6
It will "be fine", but won't maximize the benefits of having an oil cooler. The turbo heats oil up and and the engine is the one that needs the cool oil more so than the turbo. To the op, I havent seen anyone run one on the tubo feed side.