There is an Options menu, and on that is Gameplay options, and you can do any combination you want. When you do a career though, there is an Options menu in the Office while you are in port, and that is accessed by clicking on the radio icon to the left of the desk in the office. The same settings are in there, but these apply to each individual career you run, and do not affect the main menu, and vice versa. A person would use metric measure in a German campaign only because that was what the Germans used, so it is just for "authenticity". If you prefer imperial, use it.
Unfortunately, there is no way your old Save data would be usable now. Even if you had saved it aside somewhere, it would not be usable. Once the game is messed-up, the Save data is messed-up also.
Yes, the MultiSH4 v1.5 is what you use for the V1.5 of the game, which is the Uboat Missions. If you have v1.4 of the game, you would use MultiSHv1.4...
