The 4 existing axis all work fine now, both E-Stops (on control box and on the machine) work as does the tool-height-probe input and I have the ability to upgrade to 5 (and even 6) axis later.
I actually want to do that when my "SimpleMultiAxisCAM" is finished.
The dozens of inputs and the 6x 250V 6A relays are not used yet.
I'll connect the 2 E-Stop buttons and the Probe input later.
The relays will probably be used to control the water pump for the spindle cooling water and the compressor for my existing mist-cooling for metal working.
6x 250V 6A relays,
controlled via Ethernet and with proper optocouplers and galvanic isolation.
I'll not use the PWM feature as my spindle is controlled via RS485.
28 leds for all axis and inputs can e wired to the front of the enclorure.
...what an upgrade.
BTW: That breakout board is HUGE.
I also found the reson for the "stuck axis" and the "connection lost" issues.
The stuck axis seems to be a fault in the chinese MACH3 remote control and the "connection lost" a faulty USB keyboard that detaches and reattaches from USB and messes up the system for half a second each time.