Commenting more-or-less in order...

Yes, the P-CNC board does the job. The only thing I have found that would be a nice-to-have is Constant Surface Speed (CSS). Instead of a spindle speed, you specify the surface cutting speed you want and the controller adjusts the spindle speed depending on the radius at which you are cutting. So, if you are facing a large disc, say, it starts with a slow spindle speed at the periphery and speeds up as you go towards the centre. Given that this is something that most manual lathes can't do anyway, it's not a show-stopper. Apart from that, the P-CNC software and hardware seems to be OK.

NEMA34 might be a bit big for this lathe - one of the non-intuitive things about CNC machines is that sometimes bigger is not better! For example, my CNC router uses what seem to be silly little NEMA24 motors but they are happy shifting a heavy gantry. Bigger motors have much higher inertia and their inductance means that you cannot accelerate them as fast as the smaller motors. All the same, this lathe does not demand very high accelerations and machine travel isn't long enough for this to be a big deal. And if they fit... What I would ask is what voltage PSU you have - a number of "kits" have lower voltage PSUs than ideal and more volts typically means better perfornance. I'm running my original steppers off 50V AC - probably the equivalent of 65V DC or so. Again, though, it's going to work and the only downside is less than optimal performance - which probably won't matter than much. P-CNC to stepper driver connections should be straightforward.

Are there any markings on the encoder? I can't help here as I have never seen the original. My new encoder is 5V but I have a feeling that I have seen mention of the Orac originally using 12V for the encoder. Shouldn't be difficult to interface, just not quite as straightforward. Useful if it has an index output as well as AB. I think that the P-CNC will do screwcutting with just AB (no index pulse) but I'm not sure. I think I have configured mine to use the index pulse.

VFD - can you give us as much detail of this as possible? Make/model, connection diagram or photos of terminals, etc. That should help understand how to connect.