Handling is very dependent on the board. Over the years i had 4 different. The more narrow, the more insensitive it reacts on your inputs. I lately used a BIC 293 OD which i will also use for the foil. It is a little bit sensitive in speed regarding your longitudinal weight distribution, but much more easy to turn. Speed is around 21km/h at 3.5-4kW, depends on drivers weight. With the more narrow, longer boards you can also go longer distances without planning, but its hard to turn, especially at lower speed it just runs one direction: forward 
Wow that sounds quite impressive, especially for the motor you are using. I’m so hyped to esurf. I think that’s even more fun then efoil 
We will see how my plan works out.
Is it important to keep the three motor leads insulated? I mean is there any danger if they short out ?
If the cables short your esc is likely to die. If it is a “soft” short by the winding all the cables might suffer.
If the winding is not properly connected you get a higher resistance. At the 6384PG and all other motors i have bought, the winding is made of fine wires, around 30, so a single interruption is not the end.
A single short might be the end.
An opened isolation means you will be shocked if there is a second leakage and you bridge it with your hands, feet, nose, whatever. In almost dry conditions when you sweat, 12S will make it impossible to grab and turn a tool when the current goes through your hand only (not through the body). 18S is out of scope from my point of view.
I solve this problem by staying at 12S and not allowing a second leakage. And i try to avoid by constructive means to have a first leakage at the motor. Motor and mast are the higher risk. I will run the motor cable from the VESC in the battery box directly to the motor pod where i have an insulated soldering, no more interfaces like watertight 3 phase plugs. They always worked well, but are too thick.