1. Whether it supports one master and multiple slaves; 

BT02 does not support one master and multiple slaves,E74 can send BT02 slaves to the mast.

2. To transmit data to the module through the serial port, is there any requirement for the data length of one transmission, if not, is there any requirement for the sending interval of each data packet?

19200 and below can support continuous transmission. At this time, users can send data with any packet length at any time. The master sends to the slave, preferably no more than 20 bytes at a time.

The tool we use is XDS100V3.0 JTAG interface.

Around 50mA