I recently did a retrofit on my Hardinge Conquest 42, similar to your Mori. My system was all Fanuc.
I agree, talk to Mactec about the Yaskawa spindle drive.
I replaced all four of my servos with the 1.8KW DMM units and have been very happy with them. One of the servos drives the live tooling. In my case, they bolted right in with no modification to anything with the exception that I did have to build a new mount for the Z axis drive.
I replaced my Fanuc 7.5 KW spindle drive with an Automation Direct 10 HP GS3 sensorless vector drive. But because of that, I lost the spindle indexing capability, such as it was. The original indexing capability was pretty useless also, 1 degree accuracy. I have the external encoder connected to my controller, but I can't control the drive to do any positioning. I did order the encoder feedback module for the drive, but I haven't had a chance to install it yet, not sure if that is going to make much difference. It holds speed and will run constant surface speed just fine. I may just replace the spindle motor with a 7.5 KW servo motor & drive and be done with the problem. It would be nice to be able to do some profile milling and hole patterns in the lathe.
I have my spindle fan wired to come on with the control power, which powers up everything except the servo drives and the output power to the various control system relays. The turret and other functions are tied into the controller so everything is properly coordinated. I think the Oak board would be a good investment.
I can't address rigid tapping with the Centroid control, I know nothing about it. But I have not had any problem rigid tapping with my system and it is just using the encoder on the spindle.
I'll be watching your build