Bigmikeinil, I'll be interested in seeing how the printer works out for you. It was one on my short list of printers I was looking at.

According to the nwreprap site, the printer uses M5 threaded rods. That should put the steps per unit in the Z-axis the same as my MakerFarm i3v. FWIW, I have a configuration.h value of 4000 for Z in DEFAULT_STEPS_PER_UNIT. I agree with Roxy that if you think you were seeing the coupler loose at a value of 6000, it's probably still loose at any other value - just not as noticeable. The web site also says it uses Pololu stepper motor drivers on a RAMPS board. Was adjustment of the trimpot on each motor driver something addressed in the assembly instructions?

Have you went through the process to calibrate your extruder for the filament you're using? That'll affect the fourth number in the DEFAULT_STEPS_PER_UNIT values. The lower part of the vase appears like you might be under-extruding.