Connecting espruino to other espruino dynamically using bluetooth?

PS. if the USB cable is connected, bluetooth becomes Serial1, if I solder pins B6 and B7 to use the USART1 TX RX to talk to a RFduino, which Serialx do I use?

I'm not sure I understand - you can set Serial1 up to be on either A9/A10 or B6/B7 using Serial1.setup(...) - but obviously not both at the same time. You can move the console to any other Serial port you wish using SerialX.setConsole().