efergy Engage hub Sub Metering Kit

Should i combine "efergy engage hub kit" and "efergy stxtra kit transmitter & sensor" in order to submeter an outbuilding connected to same panel?

Is the efergy engage hub sub metering kit a stand alone unit? do i need anything else to read results on my ios devices?

Can the sensor wire be extended to bring the transmitter closer to the hub? If so, what is the longest distance I can extend the wire?

Does this need an electrician to install?