I'm looking at using and ATTiny9 or 10 for this project to keep the board space assemblability and power overheads down as much as possible. So keeping that in mind I have done an initall schematic in Kicad.

I have added a CR2032 battery holder and the main blink LED in the lower right side of the schematic. I have broken out the programming pins for the ATTiny and made sure there is a pull-up resistor for the reset line to avoid and funny business.

Things I'm haven't really considered a the moment is decoupling the MCU with some 100nF and 1uF capacitors. and the sew-able connections of they are an option for providing power.