New extruder calibration

Hello,
I've mounted a new extruder (direct drive,see img.n°1) and replaced the old one because of problems (geared extruder,see img.n°2).The printer is a Mini Kossel Think3dPrint3d kit (release 2).

First problem:
the extruder works in reverse direction (if I flip the stepper motor connector 180 degrees on the Arduino Shield printerboard will I solve this completely?)

Second problem:
How do I calibrate the new direct extruder? I've read the Triffid Hunter's Calibration Guide but it's been far from being clear because I'm inexperienced.If I feed 100mm of filament the measure will be too different compared to the previous calibration (the first I took on the geared extruder).I really don't know wich parameters modify in the config file...any help extremely appreciated!

SOLVED:

Just finished one simple print and everything looks working fine.

first problem:
I've just inverted the extruder connector on the Arduino shield

second problem:
I've used the simple procedure explained in this tutorial from Ian Johnson:

[www.youtube.com]

The only big difference is that the last value in the string #define DEFAULT_AXIS_STEP_PER_UNIT was much greater than the new one (around 600 while the new value after doing some calculations is only 95).
Suggestion:if you move from a geared extruder to a direct one during the first calibration take away the bowden tube and allow the filament to come out freely since the first time you're gonna extrude something between 500/600 mm so pay attention!

Cheers

Albert