3 axis mill hardware setup

mort wrote:

I am in the process of converting a manual Bridgeport mill to cnc. It will be using 3 brushless 3 phase dc motors with TTL encoders.

Do the motors have Hall-sensors, or are the encoders the 6-channel type?

So far based on my research in these forums, I have determined that I need at least the 5I25, 7I85, 7I84, and 3x 8I20 drives. I would also like to control the spindle with a VFD and add a 4th axis at a later date. Should this cover everything as far as control hardware goes?

You probably just didn't mention it, but the 8i20 needs at last 50V.
I can't help feeling that Mesa should consider making a 6pin-Phoenix to RJ45 adaptor board to simplify wiring smart-serial devices. That does rather assume the existence of a PCB-mounted plug of that type though.

Also, what benefit if any would there be with going with the 5I23, 5I22, or 5I20 cards?

No real advantage, unless the available cards suit your requirements better. My similar conversion is using the 5i23 because I needed the Resolver daughter board (and, also, I started the conversion before the 5i25 was launched)
Note that it is relatively easy to control certain VFDs with Modbus and the serial port or ethernet. (Or a USB to RS485 converter)