Adding the RAK9003 PoE hat to a RAK7244C

I realise I’m going to have to rebox the ‘sandwich’, but before I blow up the whole lot, are there any technical issues around adding the RAK9003 to the Pi + Concentrator + Cellular combo?

Is there anywhere to put a LiPo to smooth out the bumps in power requirements if calls are being made using the cellular board?