Good morning Yunus,
from my experience, at the moment I do the same, i.e. using the multi-sense module or external GIS-based tools to produce the maps of Vertical/EW motion with some spatial averaging.
About the time series, what I do is to apply use the same formula used to derive the maps applied to some specific points, manually.
The possibility to create synthetic time series from ASC and DESC data is affected by the fact that the original data are usually acquired at different dates.
In some cases for some areas in the world you may find Sentinel-1 data acquired on the same date for ASC and DESC and this makes the thing more accurate.
Best,
Alfredo