Q: Are the data stored in memory?
A: Yes, bluetooth sensor data store in router's internal memory in /tmp/.blesemd_db file
Q: Is it possible to only send the last reading of the sensor? Or from each of the various sensors I may have?
A: There is option to set emit period to 10s in bluetooth sensors and set 10s period in data to server feature, that way router will only send one string of sensor's data to server. If sending period will be set to 60s, then router will send 6 strings of sensor's data. Unfortunately, currently there's no option to select which of stored data will be send and router will send all collected data.