A 1610 with a 2:1 belt reduction would be more than adequate given your low speed requirement, or even direct couple a 1605 to the motor shaft. More than enough linear force to handle 125 lbs.
Given your low accuracy, low speed requirement, I think a flange bearings would do fine. Not really designed for thrust, but they will actually take quite a bit, much more than the assembly could exert on it.
Now the real problem, how are you going to keep the abrasive clay off the the ball screw, and out of the lower bearing? That alone would cause me to look in another direction. My lathe has an extensive sliding shield system to keep the coolant and chips out, but the Z axis on my Haas mill has an exposed ball screw on the lower end and it does get splashed with coolant & chips, but that is really a pretty non abrasive environment.