New Machine Build- Jet 1600 ZX (2004) Manual to CNC Conversion

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I've got a machinist friend who is looking at replacing, for the 3rd time, some plastic gears on this Jet 1660 ZX that help with threading. While talking to him, he mentioned that maybe its time to take the plunge, and go CNC. I don't use a lathe, but i have a homebrew >8' x >5' x 6" CNC router. I figure i know the electronics to some degree (I use steppers), but i told him that his best bet was to get on here, and get some help from those who actually know what they are doing.

He hasn't got an account yet (Should be getting one this evening), but i told him i'de start the thread (and send him a link), and kinda be his "spiritual helper" during this "Conversion" of his

So, he has a JET 1660 ZX (2004 model). He wants to automate it. Please, anyone, chime in with anytime on this. I'll get the ball rolling by asking questions he may not yet know to ask.

First,
Where should we start? I figure if he's going to do threading, and if the machine currently uses gearing to ensure that the threading all lines up, then we will need to get feedback about the rotations of the lathe in order to get the computer to run the steppers feed correctly. I am no expert, but my initial thoughts are:

Somehow put an encoder on the Headstock to give feedback to the Computer concerning rotation/positions (everything an encoder can tell the computer).

I know Mach3, so thats the control software i would recommend, unless someone else has reasoning for why i might use something else (is there anything else? EMC2?)

We'll need to have the controller running the feeds. How many are we going to need for a lathe? There is along the length of the material (along the axis of rotation) (i think of that as the X), The Y (Maybe this is what is called the cross feed?) Forgive me for knot knowing Lathe terminology.

I am comfortable with Steppers, but maybe we would want Servos here? Anyone know how we can determine what we need. I know allot of it has to do with, How fast do you want to go, and how much do you need to push.

I'm guessing that he'd need to introduce the stepper inplace of the gear that ties the rotations of the headstock to the feed, which would put the feed in the hands of the controller. Secondly, that he would need to put an encoder on the headstock.

I'm planning on being his expert on this, and we hope to plan it out pretty well before moving forward. Hopefully i know enough already to get a jump start for us.

I think top priority right now is, Get the ability to feed, and the ability to do threads back, via CNC (The broken gears are for threading, and if he is gonna spend money, he might aswell use it for an investment instead of replacing a part that keeps breaking). So, anything other than the Feed, and encoder for the headstock is probably on hold to be done as a Modification After the fact.

I recon many of yall will already know that
"so and so already did that here:", or so forth, and will be able to direct us to the reading we need to get "up to speed", without needing to read 4 years of a thread to get to the "point".

Thanks ahead of time.