is it possible to connect the accelerometer and the bluetooth module on there own with a power supply?
Not in any useful way. The bluetooth device transmits serial data. The accelerometer does not output serial data.
is the smallest increment an RTC measures in a second?
Measures? No. Reports? Maybe. Depends on the RTC.
can i send multiple sensor data to the same SD card?
Data is data. Doesn't matter where you got it. Of course you can.
or save to the SD card with time in a column next to it.
Absolute time? Or relative to some event, like the Arduino being reset?