Take a look at my Attiny 167 core:
It provides full support for using the 167 with the Arduino IDE, and provides a version of optiboot that is compatible with the weirdo LIN UART in the 167. The 167 doesn't have hardware bootloader support, so it uses virtual boot - the impact of this means that if using the bootloader, you can't use the WDT to generate an interrupt. For this reason, you may prefer to use ISP programming.
Only external component you need is the bypass cap. I would be inclined to add a larger cap across the supply for good measure, something around 10uF. If you want to use bootloader, you will need a cap for the DTR autoreset trick and resistor to vcc on reset. If you don't need autoreset, you still might want to use the resistor.
Have you considered the ATTiny 1634? It's got a USI that you can use for I2C master, a second UART (but it shares a pin with the USI...) more RAM, two more IO pins (only one Gnd and Vcc pin), is available with the 2% factory calibrated oscillator, and is IIRC cheaper than the '167. You can also get them in the MLF package, which is super tiny - SOIC-20 is huge next to MLF-20.
Anyway, my core supports 1634's too, with bootloader, same caveat.
I also sell breakout boards, bare and assembled, for both those parts (in SOIC-20) at my tindie store.