What length wire and how many devices after which I need a repeater or extender for i2c?
You need to check the total capacitive load with the pullup resistor values for the RC time constant check if the rise and fall time (3 time constants long) are enough for your data rate.

Smaller pullup resistors are faster and can work with more capacitance but cause more current to flow through the pin when it drives the line LO, so you can't go too small.

Active pullups also exist, not just buffers, repeaters, or extenders. They replace the pullup resistors and are a constant current source so no RC time constant.