This is awesome. Many years ago I tried making an Android app for uni that would help you point your phone at the star you selected. The maths for that was insane and way over my head, I can only imagine that satellites would be much harder.
Such a cool use of everyday tech!
There are libraries built with all of this math done for you already.
Astropy, orekit are two I recall from memory, but there are more
It might actually be easier since they have know trajectories and velocities with a easy to calculate schedules.