The answer to your fuel question will depend on your game play setting.
Without limitless fuel you will be dead in the water literally.
Post #61 Game Play Settings In Silent Hunter 5
The answer to your imperial/metric question also lies in the game play settings.
How accurate the transition is I do not know as I have always played American SH4 with imperial and German SH5 with metric measurements.
Post #12 How To Change Your Game Play Settings In The Bunker
Peter