OK,to start at the beginning with each of your points, cracking near the screws is poor, shouldnt happen and needs to be replaced regardless of what the 'manager of VE (vision express) says.
Second point, if they scratch the lens then they should replace it.
Third point the optical screw, this tbh is forgivable, these things are tiny and if dropped can be very difficult to find (we use magnetic mats to try and prvent this, but sometimes still lose one) but should be replace with one as similar as possible.
With regard to the third point , i would need to know your approx prescription to be sure, but it sounds like the rear surface curve of your lens is too great for the curve of the frame (this could also be the cause of point 1 above). I good opticians can ask for the curvature of a lens on the front and rear surfaces to be adjusted to suit certain frames.
I personally wouldn't be happy with the above job, but having said that you go to the high street 'factory' shops and you pays your money and takes your choice as the saying goes