I haven’t actually shared the ball screw build/design yet, I still need to verify that I fixed a clearance issue in a design iteration before I upload these mod additions 
but have been using the machine for about a year now with the ball screw supports orientated in this position no problem.
Were you annoyed as I to find that the bolt pattern and diameter are different between the FF and FK?
The inductive sensors came from Centroid’s recommended list (amazon special), I bought my SO3 before the inductive and Z-plus days and prefer normally closed (NC) operation anyhow. I can’t recall the repeatability I was getting but I can measure it soonish (my cnc computer went down and is getting repaired under warranty). I can say, as I use tool offsets that depend on Z home and tool probe, I would see less than 0.001" deviation (usually 0.0003-5") on tool offset measurements, this would be stacked repeats of the Z homing and tool probe trigger.
I would probably suggest a limit switch + Z/I pulse for a build like yours. Initial homing triggers the limit switch (inductive, mechanical, optical) and then the back-off movement looks for the first Z/I pulse on the encoder to stop and set machine home. Remembered wrong, that was Moded1952