Startup trouble

So electrically I would take 5V from TB1, route it through TB3 14 & 13 (OUT0+/-) to EN+ on the TB6600 and back from EN- to GND on TB1.
How do I get the Mesa card to switch OUT0 when I move an axis?
And is this worth the effort or just something you live with (with those drivers)?

Yes, you could do it that way, typically you would enable the drives
with something like motion.motion-enabled

I guess I'll have to read some more docs until I understand what I have to do for the enable.

The step pulse of 40000 is not a problem?
I need about 80 steps per mm and 33 mm/s max speed. That is from the old grbl config so that should already include the microsteps.
80 x 33 = 2640 steps / s => 378 µsec max time per pulse. If the step pulse setting is at 40000 that's 40 µsec so I should be good, right?

Yes, that should be fine even with step length and step space = 40000