Thanks! I will try the simple one today. Will also check which resistor is the maximum - will breadboard 1k resistor and a 10k potentiometer in series, and see how far I can turn the potentiometer until the comm breaks up. Will probably initially try the setup with Unos, as its easier to use them for breadboard due to full size usb and also connectors for prototype wires, and I can use two of them same time, while I will need to swap ProMinis, as I have only one programmer for them.
Is there a guide how to program ATTiny with Arduino?