Definition Slave and Master Images in a set of images

I meant it depends on the technique you’d like to follow, in case of PSI, you’d need at least 12-20 images, however following the DInSAR technique at least two images should be processed, and so on concerning the other techniques,

I think preparing and processing series of S-1 and ENVISAT ERS… have been mentioned for example
under this topic, you could find a lot of things

How to prepare Sentinel-1 images stack for PSI/SBAS in SNAP 5