RE: Mono hull rudder and turn fin questions
as for sharpening rudder or turn fin they should have a nice slim front edge
to knife blade them it will make the boat very twitchy to steer most guys round the bottom front of rudder like a 5 mm radius makes for better entry an reduces drag
as for turn fins position them at a roughly 90 degrees to bottom of boat is a good starting point even around 110-120 works good depends on boats corner speed an type of hull
some boats do not even need turn fins