Hardware advise mesa boards for contol-loop with motor-encoder and linear scale

Hi. 
Recently I bought a mechanically immaculate Maho500c milling machine, but with 41jear old electronics.....

I want to strip the machine from the DC-motors, drivers, philips glass-scales, and the philips 432/9 controller.

But then, I cannot ma a choice between all the (FPGA) controllers, servo-drivers, communication protocols like analog, step-dir, ethercat.....

I'm convinced to have the best options with LCNC, also because my machine has a gearbox which is already solved.
One demand is, that I keep the closed-loop to the new 1um glass-scales and also the option to controll 4 or even 5 axes full simultaneously.
Choose for accuracy before speed, because the machine isn't capable for high-speed.

My first plan was to choose for a 7i95T board, or what in case if I should choose for ethercat?

I already read a lot of threads, but have troubles to know the current statusses of all projects in parallel..
Who could provide me some good advice, given the latest developments and experiences..
With kind regards, and already thanks,
Joseph.

Note that whatever control hardware is used, tuning will be problematic
unless you can remove almost all backlash from the mechanical system.
 

Thanks.
Do I read between the lines, that you think it hardly makes sense?

If the hardware would be “perfect” with no backlash at all, there would'nt be an necessity for linear scales… And with backlash it is “problematic”.

Originally, the machine had tacho’s on the motors, to detect the motors were spinning and to control theirs rpm... Based on the position measurement of the linear scales (distance to go), the loop was closed until position was reached.

Would that principle be different if I would use step/dir instead of analog +/-10VDC in the old situation? The resolver needs at least 10x higher resolution than the 1um resolution of the linear scales I presume….

And is there then a necessity for a drive with two resolver inputs? Or can a controller-card take over the correction of backlash (which will be in any case)
Do they even exist without paying the highest price?

There is really no control mechanism that can compensate for backlash
in a very satisfactory way, especially if the cutting forces can reverse.

Linear scales can compensate for ballscrew thermal growth, and flex
in the drive system in response to acceleration and cutting loads.
With any system you would need a way to read the scales and combine
the scale information with the main position loop.

Typically 2 PID loops would be involved as the tuning of the scale feedback
would have lower bandwidth than the much more tightly coupled rotary
encoder feedback.