Re your prop and it’s angle!
I agree with Martin…..motor and shaft in my experience should always be in line and as straight as possible.
Whatever type of coupling you use the more you increase the angle in relation to motor and shaft the more you increase the friction/drag and potential noise from the coupling.It also drains the battery with the heavier load
I attach a picture of an example that is in build by me at the moment.(Starting a blog soon)it shows the shaft and motor in as good a line as possible.
The greater the angle of the shaft will also push the bow down at higher speeds.You can compensate with counter weight at the stern,but that will make the boat sit deeper in the water when stationary and again adds more weight.
If your rudder is too close to the prop and you are running at high speed then you risk cavitation from the prop(Air bubbles) which could affect the rudder efficiency.
All my boats run at relatively slow speeds so not a problem for me.
I also try the keep the rudder post close enough to the prop so that if the prop unscrews(which it shouldn’t if you use opposite tread to shaft rotation) then the post stops it falling off.
We are away at the moment on holiday and if the wife catches me on here too long I’ll be in the soup,so more when I get home.😂
Hope it helps.