Where is the fountain of knowledge for learning about CNC setups / understanding them

[Neale]

I'm guessing from the Mach3 settings that you have 5mm lead ballscrews with 8x microstepping in the stepper drivers. That explains the "320 steps per unit" in the motor tuning page. That's about right, but you also need to check the drivers themselves to make sure that they are also set to 8x microstepping to match. If they are set wrongly, you might be trying to move the machine much faster than you expect. The drivers normally have a little table on them showing DIP switch settings.

As long as that's correct, Nick's advice in the previous post is spot on - you can do as much analysis and design as you like, but at the end of the day we all just gradually crank up first speed and then acceleration until the machine starts misbehaving, then back off a bit for safety.