@tedey Do you mean you bought a PanelDue? Most other LCDs are not supported. For PanelDue cabling, see https://duet3d.dozuki.com/Wiki/Connecting_an_LCD_control_panel#Section_Option_2_4_way_cable
The length of the 4-way cable is not critical, however the resistance per conductor should not exceed 0.1 ohm. The SD card socket on the TFT panel will not be functional. The cables supplied by Escher3D and Duet3D are about 800mm long. There have been reports of cables up to 1500mm long being successfully used. Take care to route the cable away from motor and endstop cables. Twisting the cables may help prevent cross talk interference.
Using 18 AWG (0.823mm^2) copper wire should give a resistance below 0.1ohms over 3 meters, but it may be worth using 16 AWG (1.3mm^2) for lower resistance. Make sure you make the crimps and connections well, too. Let us know what works!
Ian