PWM on the LED?
something that is built to use to I/O pins for bit-banged I2C device emulation
Is there a reason you do not want to use hardware support for I2C?
The ATtinyX4 family has a "USI" (Universal Serial Interface). BroHogan has provided this for the ATtinyX5 family...Looks to me like an ATtinyX4 would work very well.