Extra I/O means thet the 8 pin IC is not able to drive any load beyond a logic IC. So it needs either a higher gain transistor or a buffer IC in order to do anything useful. . And it needs something external to tell it to start. And it probably needs a crystal and 2 capacitors for the clock oscillator.

I don’t understand the need for an external clock oscillator. The ATTiny 8 pin MCUs have internal clocks.

And I’ve never needed external components to tell the MCU to start?

My previous post included components for driving external loads. I have completed projects that use 3 drivers with couple of resistors and a 2N7000 per pin, to drive three loads.

So, in my experience, most of what you refer to is not necessary.

 

Ah right ya forgot to mention the voltage supply is essentially coming from a pH probes voltage im boosting. (with batteries but very unstable)

The pH probe question is on a different thread and I try my best to avoid tangling threads. I try to focus on a locus.