If you bought breakout boards with sensors, those boards have many times pull-up resistors.
You don't want too many pull-up resistors.
If that happens, use 4k7 pull-up resistors and remove the pull-up resistors from the breakout boards.
About twenty I2C devices on the bus is no problem. In theory it can be many more. Too many long wires could be a problem.
All sensors should be powered, for example with 5V or 3.3V, independent of the I2C bus.