7i96S + 7i85S + 7i84U for a 4‑axis mill: compatibility check before ordering

Hi all, I’m planning a LinuxCNC retrofit of a small mill (HM‑46B, a RF-45 style machine offered in NZ & AUS)  and want to confirm a Mesa combination before I order. Ive done what I can with reading the Mesa site and here, + a bit of help from claude. 

What the machine needs:

• 4 step/dir axes (X, Y, Z, A), external stepper drivers
• 6 encoders: one per axis, one MPG and one spindle encoder
• Analog 0–10V spindle to a VFD
• About 20 inputs and about 10 outputs at 24V

Planned hardware: 
Ive got 2 options in looking at, which ive called A and B:

• A -  7i96S + 7i85S + 7i84U + DB25F-IDC26 cable
• B -  7i95T + SPINX1A + Modbus relay
I would greatly apreciate it if anyone can comment on if either setup would work for my machine, and if the firmware already exists for this setup. Im leaning towards A as it keeps everything running on mesa, and the 7i95T is current out of stock (So is the 7i76EU ).Ive already ordered a HP i5 Mini PC, the specs are : Processor: Intel Core i5-8500T (6 Cores)Memory: 8 GB RAMStorage: 256 GB Fast SSD  

I would probably choose a 7I76EU and add a 7I85/7I85S if you need the encoder feedback
(encoder feedback on a step/dir systems normally is not needed unless you want to add 
linear encoder feedback.)

Even though its out of stock, the 7i95T : I would check if your spindle servo drive accepts step-dir as well, in which case 5 axis+feedback and 1 spindle still fits on one board without additional, though the IO will be your bottleneck.

Yea should have said, I want to add linear encoders.

Probably should clarify my setup, I have steppers on my axis and am going to add linear encoders on each axis. Spindle will be a VFD on a 3 phase motor, with an encoder to check the speed.
The reason I was going towards the 3 boards is also so i get all the IO i need. And since its in stock now I can start wiring it all up over summer/christmas leave

If the 7I76EU (Or 7I95T) stays out of stock for a while, would the 7I96S + 7I85S + 7I84U work as a fallback? Specifically, is there existing 7I96S firmware for a 7I85S on the expansion port? And is there an ETA on 7I76EU stock

The 7I76EU is in stock at Mesa and at least some of Mesa's dealers.