Hi there, thank you all for the replies.
@PaulS -
So if bluetooth transmits serial data and the accelerometer doesn't give that, then i would need something like an arduino nano to convert it to serial data before bluetoothing it across to the main board, connected to the computer and SD card?
And to your last question, i need the time in either milli or micro seconds (hence the question about the RTC) from the point the accelerometers are told to start measuring/ data comes in. In Jeff Rowbergs code for example, it says "Send any character to begin DMP programming and demo:". I need to measure from that point. Currently i am just subtracting the first number in the data away from everything else.
Would using multiple accelerometers mean that to print the data to the serial monitor they would have to be called as MPU1, MPU2 etc?