Hi @ABraun,
in the project.conf, the paramter MASTER must contain full path to the splitted and orbit corrected (preferibly with precise orbit information) master image in dim format, and it is suggested to put it in a separate folder (otherwise in the coreg-ifg step it will try to process it),
It could be for example:
MASTER=/home/pi/Desktop/PROJECT/master/S1A_IW_SLC__1SDV_20150405T175350_20150405T175417_005352_006C9E_0FE9_Orb.dim
The processing of TOPSAR-Split (with the minimum bursts of a single subwath covering your AOI) and ApplyOrbit should be done by now using SNAP GUI (so you can identify your AOI visually)
Indeed a sample of a full test could be included in the SNAP2StaMPS_User_Manual to put everything clearer.
I hope this helps.