First time user - how to seup BLE message on my MDBT42Q,2v04?

run a scan once every second and get the signal and mac of the around and save it to the device.

Just call http://www.espruino.com/Reference#l_NRF_findDevices and it'll call back with the devices that are found.

It's worth supplying a filter though as if you run it somewhere busy you can potentially get so many BLE devices it uses up your available memory :)