I am glad that you can use the snap2stamps package and you find it useful! Please do not forget that it uses SNAP for doing the job, that package is only a wrapper to automate the processing.
For the mt_prep_gamma, you need to modify the existing script, maybe make a backup and modify the lines:
calamp calamp.in $width $WORKDIR/calamp.out s 1 $maskfile
mt_extract_cands 1 1 1 1 s 1 $maskfile
calamp calamp.in $width $WORKDIR/calamp.out f 1 $maskfile
mt_extract_cands 1 1 1 1 f 1 $maskfile
s changes into f , because the SNAP gamma format is float complex and not single complex.
Regarding the ps_load_initial_gamma I do not remember to had modified it. So it should work as it is. Let me know if this is not the case and I will share my mt_prep_gamma and ps_load scripts.
Regarding DEMs, indeed the use of a more accurate and updated DEM is better, but it becomes more important when working with higher resolution SAR (X-band stripmap for example). Indeed there are many DEMs that could be used, ie: SRTM DEM (3 or 1 arc second), ALOS DEM, TanDEM-X, etc , but always in GeoTIFF for being used using SNAP.
Enjoy the snap2stamps scripts!!