sorry, I misunderstood you. Yes, 30 are enough. You can use the ASF baseline tool to identify the most suitable master for your images: https://baseline.asf.alaska.edu/#/baseline
I had best experiences by firrst searching one of your used images in ASF Vertex: https://vertex.daac.asf.alaska.edu/
Once you have the list of results, you can click on “View Baseline” for one of your images at the correct footprint/granule and then you will be redirected to the ASF Baseline tool which already lists all Sentinel-1 images within this footprint. Then you simply have to adjust the temporal span and click on one of the images which is most centered in your graph.