I wrote down the plan based on all the thoughts and little sketches that were scattered around my desk.

Explanation:
The robot arm has six stepper motors for its six degrees of freedom (DOF). These motors require drivers, so I will use six TB6600 stepper motor drivers. I chose them because they are reliable, can handle the voltage and current required by my stepper motors, and I already had bought six of them for this project.
I also tested TMC2209 drivers from BigTreeTech, but I could not get them to work reliably with my Arduino and the stepper motors I bought. During testing, I also fried several of the drivers.
The stepper drivers are controlled by a motion controller based on a Raspberry Pi Pico. It calculates the required steps and speeds based on commands received from the RP5 via USB and sends the corresponding STEP/DIR signals to the drivers.
The Raspberry Pi Pico is powered through a DC-DC buck converter. I chose this setup because I am concerned about potentially damaging the RP5.
The Pico is also connected to seven limit switches, which are used to home the robot arm. I have seven switches because I had one pin spare, which I plan to use for another function later. In addition, the controller has an enable-control LED and three servo outputs, which I will need for additional functions and could connect because I still had three GPIO pins available.
The six stepper drivers are powered by a 500 W, 24 V, 21 A power supply.