What happened to the 128 servo motors in your previous topic ?
Please don't limit yourself with the Uno as Master. Use a Arduino Mega 2560 for the Master as well. That will also make it easier to change to Serial/UART communication.
The maximum sink current for the I2C bus is 3mA. That is the current that is needed to pull SDA or SCL low. Each Arduino Mega 2560 has onboard 10k pullup resistors. You have to remove a number of those, or you can remove all the pullup resistors and use external pullup resistors.
The Arduino Mega 2560 is a 5V board with a 5V I2C bus. The pullup resistors go to the 5V pin.
The I2C bus is a weak bus. It has three wires: SDA, SCL, GND. You should be very careful with the GND that is used for the I2C bus. If the currents from the stepper motor can somehow go to that GND of the I2C bus, then the I2C bus will no longer work.
Are your wires 20/30 cm to each Slave ? So the total length of your I2C bus is 2 meters and 25 centimeters ? Then you are in for a lot of trouble.
Dear rr1991, you should reconsider your project. Such projects are in theory not impossible, but we see them often go wrong, both in software and in hardware. Paul_B and lastchancename know what they are talking about and I share their concerns.