Not sure about the screen.. or what you'll need to control/communicate with it..
but the rest sounds like normal project stuff...
SD card will use SPI..
Bluetooth will (most likely) use SERIAL
Pro-Mini's are smaller.. unless you dont care about having a HUGE watch on your wrist! lol.
you might be looking at making a custom board if you really want to fit this all in a watch.. with all SMD components.. (and even then.. it might not be as small as you think)