I2C pull-up to multiple voltage question
You only need one pair of pull-up resistors for entire bus. Adding them at each node will create too strong pull-up.

This, consequently, answers your other concerns - you can connect pull-ups to any 3.3V source and be OK.

However, there is a caveat - most MCU and other I2C devices have maximum pin voltage specified relative to VCC, e.g. "VCC + 0.5V". This means that if any device on the bus loses its power for some reason its pins will immediately go beyond maximum allowed range.

The pull-up resistors will limit the current, hopefully preventing burn-outs. But for maximum reliability I'd suggest using one big 3.3V supply to power all devices on the bus and provide voltage for pull-ups too.