the question you ask is no longer related to the topic of the thread, please consider this before posting to help keep the forum as structured as possible.
InSAR is a complex topic, make sure you are familiar with the basics, reading this is a good start, furthermore study paper and learn from good published practice.
PS will provide you with less points then SBAS to track, but still using PS or SBAS is not the whole question, which algorithm you use (SqueeSAR, StaMPS etc.) changes a lot too, mainly during phase unwrapping and point extraction, as I know. The area of your study site and the topographic conditions are very important, using plain StaMPS in high mountains could become a problem, and in general, if you can answer your question with the less processing intensive and complicated approach, I would choss this (Occam’s razor)
Concerning de- or ascending orbits, it depends on the orientation of your slope. Choose the orbit where the radar looks down the slope, for ascending and right looking radar these are slopes orientated to the east and vice a versa for descending. This omits foreshortening but if your slope is to steep, you may have problems with the radar shadow…you can analyse this beforehand with a DEM and I think there is a tool in SNAP doing this too. To decompose LOS movement to vertical and horizontal movement you should in the end use both ascending and descending orbits, have a look here.