I'm already doing Arduino programming for a high-altitude balloon payload. Perhaps I can help. I just weighed the Arduino UNO plus adafruit data logging shield (Adafruit Data logging shield for Arduino [v1.0] : ID 243 : $24.80 : Adafruit Industries, Unique & fun DIY electronics and kits) plus 4GB SD card. It weighs in at 48 grams. Do you need something lighter then that?
Your pressure sensor looks good. It should measure in close to 0.25 millibar increments. I have not use the I2C (Wire) bus before but it doesn't look hard.