Hi ttomy,
I'm from Germany (the very south) and the average height is exactly 180cm as well.
I'm only 161cm and I'm going to lengthen 9-10cm, split into two surgeries, which seems to be the maximum for my body proportion-wise.
Since your starting height is ~167cm, I think your personal max. would be around 10-11cm, without making you look odd to others.
But it depends on your body/appearance and numbers about your proportions are only indications.
Your goal to lengthen by "just" two inches, sounds very reasonable to me.
It could be done on just one segment, tibia or femur.
Tibia is easier and there is a rule of thumb to not lengthen your shins more than 5-6cm (your desired 2 inches).
Femur can handle a little more lengthening.