I love this so much. Is there any open-source software that calculates where a given planet or star might be (based on your coordinates) and automatically finds the star / planet and then follows it? Can these mounts be used with such software if it exists?
> Is there any open-source software that calculates where a given planet or star might be (based on your coordinates)
Sure. Skyfield is a python library to calculate that (among others). Right on the front page is an example how to calculate the azimuth and elevation of Mars: https://rhodesmill.org/skyfield/
Yes, the OnStep firmware used here has drivers for ASCOM and Indi, which are communications protocols commonly used by most astronomy software on Windows and Linux. It also speaks the older Meade LX200 serial protocol, which is another common method.
For example, Stellarium on your phone can connect to the mount’s wifi station and control it.
Stellarium and Kstars (which has EKOS built in) are both very good planetarium software. Both can interface with indiserver, which can talk to many astronomy devices such as mounts, filter wheels, cameras. I use Kstars mainly for controlling the mount, and Stellarium mainly for finding nice targets.