[TRY]

I would say that a 25kw engine would be sufficient since we have a better torque than an electric engine.
Weigth and size would be some 25% of a diesel engine (since we have NO ancillary equipment hanging around the engine), tanks can be place anywhere, according to required autonomy.

Noise will be almost zero if you allow for a decent cocoon (no heat is developed).
As long as the engine runs you get free cooling from the exhaust.

Cost will be less than half of a diesel propulsion (engine, ancillary, tanks, all included that is).

You will fill up in any mooring or marina with a standard shore power socket.