Power consumption was also my concern. Still not sure if I will use AA or AAA batteries or go for the coin cell. I suppose it depends upon the final direction of the project. Could end up self contained unit or a unit with Bluetooth LE control from iOS, or both.
You've definitely piqued my interest regarding the STM8 and STM32. I'll have to give them a go in a few more months. Looks like an STM8S discover board is only $7.84. Cool stuff. Thanks!