And don't assign anything to the main throttle axis group. Use custom axis groups instead.
When testing for best speed it soon becomes apparent that there is a very narrow window for optimum prop pitch. You will either need to get lucky to find this optimum setting or have switched on fine control (caps-lock). Main throttle keys do not seem to respond to the use of fine control but custom axis group keys do respond.
As an example, if I takeoff and have rpm limit on the main throttle the smallest change I can make with or without fine control is 4 rpm with a sharp tap on the throttle keys. With rpm limit assigned to a custom axis group, the smallest change I can make with fine control switched on becomes on average 0.2 with the same sharp tap. With prop pitch on a custom axis group the smallest change I can make is 0.5 (or two taps to make a change of 1). Best speed is achieved within a prop pitch window of 0.5 - 1.
After takeoff, reducing prop pitch will usually increase speed until a point is reached where either the speed starts to drop or the current rpm (not the rpm limit) starts to drop below 460. The value of the prop pitch at this point is worth remembering. When starting a sharp turn or a steep climb it may often be worth changing the prop pitch back to this value. Effectively you can control airspeed and power by only using the prop pitch.
But you need the current rpm to drop in order to reduce prop pitch to achieve the fastest speeds.
If say, in level flight, the current rpm does not start to drop and speed reduces when you reduce prop pitch from this value, you can force it by reducing the rpm limit and further reductions in prop pitch should see a marked increase in speed. At some point the current rpm will usually drop below the rpm limit. Quite often though, the current rpm will drop by itself leaving you to concentrate on finding the optimum pitch for speed.
When trying to find the best settings for maximum range, only two things seem to affect fuel consumption - rpm limit and torque limit. Again it will be a benefit to be using fine control with nothing assigned to the main throttle keys.
I find landing to be pretty easy. I reduce rpm limit and torque limit if for no other reason than making sure I don't run out of fuel before landing then on final approach, increase prop pitch back to 100 and drop the landing gear. Speed drops dramatically but flying in under power still provides good control.
All robotic engines can have an action group key assigned to toggle the motor direction. So on touchdown, reverse the engines until stopped or nearly stopped then use another action group key to toggle prop deployment. This is much safer and much more effective than using brakes.
Like @aegolius I disengage the engines in the SPH so my usual setup is something like this
Action group 1 - Toggle engage engines
Action group 2 - Toggle engine power (full torque on/off)
Action group 3 - Toggle prop deployment
Action group 5 - Toggle motor direction
Custom axis group 1 - prop authority
Custom axis group 2 - rpm limit
Custom axis group 4 - torque limit
So takeoff is as simple (after engaging SAS with the 't' key) as 1,2,3.
If you want to see a hard to land plane, you can check out the landing at the end of the video below which was made for the Kerboprop Speed Challenge - which requires a landing back on the runway. And it wasn't hard. The optimum prop pitch for speed with this plane is 29.5 - note that the current rpm is only 220.7 at 298.6m/s - while the value for the prop pitch I use to maneuver is 70 and you can see me increase it back to 70 as I start the vertical climb preparatory to returning to the runway and then back to 100 just before landing.