Here is my slic3r start code with homing and pre-heat and priming line.
M82 ; Extruder in absolute mode
G28 W ; Home extruder
G1 X0 Y0 Z5 F{Z_TRAVEL_SPEED}
M107 ; Turn off fan
G90 ; Absolute positioning
M104 S150 ; start extruder heating
M190 S[first_layer_bed_temperature] ; set bed temp
M140 S[first_layer_bed_temperature] ;wait for bed temp
M109 S[first_layer_temperature_0] ; Wait for all used extruders to reach temperature
G92 E0 ; Reset extruder position
G1 X5 Y5 Z0.25 F1000.0 ; go intro start pos
G1 X60.0 E9.0 F600.0 ; intro line to prime extruder
G1 X100.0 E16 F800.0 ; intro line
G92 E0.0 ; reset extruder distance position