Replacing MB, what do I lose/keep?

Hello. Recently my 5x was badly damaged. All of the outer components of my phone were destroyed and all i'm left with are the internal pieces. I bought a replacement phone but have some things on the older device that im unable to reproduce.

My question is if i take the mother board of my broken device and replace it inside of the new device, what all data (app data, photos etc) would be lost or carried over if anything at all? Would it be like getting a new phone or picking up where i left off with the broken device?

Alternatively could i possibly recover data by simply swapping the memory chips on the divices without changing the whole MB assembly?

Just looking for the best way to recover potentially lost data.