M552 S0 = turn off networking, you do not want that in your config.g if you want networking.
config.g that contains this should connect if a ssid and pw is previously set.
; Network
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet
Be sure the network is 2.4GHz and not a 5GHz one, since the 8266 module only do 2.4GHz iirc.
I find Arduino IDE serial monitor really quick and easy to use to talk to Duets and other boards, it has a drop down menu to set line endings and baud rate on the serial window.
from the gcode wiki:
M106: Fan On
Parameters
Pnnn Fan number (optional, defaults to 0)
Snnn Fan speed (0 to 255 or 0.0 to 1.0))
Your Macro turn the fan to a very low PWM duty cycle ( M106 P0 S1; Power On Fan )
Notice S1, that will be 1 in the 0 to 255 range, you need a 1.0 to use the 0.0 to 1.0 range.
Either try:
M106 P0 S1.0
or
M106 P0 S255
for full speed.
Your multimeter probably reports peak volt, you can verify with a little capacitor in series with your probe to even out the pwm signal, if you do not have a oscilloscope. (with S1 you probably get a low volt value with the capacitor in series).
M552 S0 = turn off networking, you do not want that in your config.g if you want networking.
config.g that contains this should connect if a ssid and pw is previously set.
; Network
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet
Be sure the network is 2.4GHz and not a 5GHz one, since the 8266 module only do 2.4GHz iirc.
If you have a multi meter, measures resistance between the motor phases. On your motor 2 and 2 phases should have similar resistance (probably around 0.9 to 1.5ohm) but from one phase to the other there should be really high resistance (mega ohms).
Once you have identified the phases, connecting them should be straight forward.
One way to rule out any mechanical problems is disassemble the motors from the printer and just have a piece of tape on the motor shaft and test if everything moves the correct direction(remember to never connect or disconnect a motor when the driver has power).
Your Cura print seems to have to little retraction/too high temp and probably a line width that is not dividable with the model wall thichness since there is so much travel moves on this simple model, you can check what causes the travel moves in the preview (turn on travel moves).
A slight change in line width can do wonders when you are working with a scaled or a model with a thickness constructed with a different nozzle size in mind.
Just as a note on under extrusion the direct extruder on the wanhao i3 2.1 & plus has a quite dull gear as standard, it is a quite easy upgrade to exchanges it for a mk8/mr10 style one, just remember to recalibrate exstruder steps afterwards.
Power down and disconnect power, then do a continuity check for both ground and 12/24V with a multi meter on all the cables that goes to the print head, to check for shorts. The thermistor for the heat bed is also a good idea to check for a short to 12/24V.
This movement only happens when you probe your bed? If that is the case there is probably a probe offset(G31) in Y set somewhere, since the i.e:
G30 X100 Y100 uses position of probe(nominal tool holder position & probe offset) , where as
G1 X100 Y100 uses active tool position(nominal tool holder position & tool offset).
Check your config.g, homeX/Z/Y.g and Bed.g for any G31 with a XY value or G10 tool offset in XY.
For multi material I guess this is the ideal solution atm. E3d Toolchanger All the files are on their github if you prefer building it yourself instead of buying. E3d Github.
A tip would be to consider what kind of material you want to print, like do you need an enclosure and how easy is that to incorporate for the design.
Consider the importance of print speed, a hypercube with a chimera will require lower accelerations, since the print head will be heavier.
PanelDUE works fine on a RADDS board, iirc the pins in the connector had to be rearranged to match the top 4 pins in AUX1. I had to solder pins to AUX1 as well.
Firmware 2.03 works fine so far 
Send: M115
Recv: FIRMWARE_NAME: RepRapFirmware for RADDS FIRMWARE_VERSION: 2.03 ELECTRONICS: RADDS 1.5 FIRMWARE_DATE: 2019-06-13b2
There is a lot of sdcard juggling between the printer and pc when setting it up.