Really fascinating ideas! I would think that one of the difficulties would be dealing with expansion of the plumbing. Anything using flexible hoses will have to deal with this issue.

It might be easier to solve with small 3-D printed digital parts (AND, NAND, etc) that could be fitted together with rigid PVC off a plumbing manifold.

This might allow you to make smaller parts also.

I think you’d also need some sort of hydraulic expansion tank that would act like capacitors - necessary for storing memory and improving signaling.