Arduino boards typically don't have a DAC, but it's a common enough feature in microcontrollers that I figured I'd mention its absence.

Arduino Uno no, since that uses a chip that is over 8 years old. But a modern 8bit AVR which cost under 1USD in single units, like Attiny3214, has a DAC.

You can bit-bang I2C easily enough, as long as none of your slave devices have an SMBus-style bus timeout feature. Might be a bit hard for an AVR-class CPU to keep up with those without some attention paid to performance optimization.