Is there a way to know what features have already been requested before I submit a request?

You can see that on github. https://github.com/dessalines/jerboa/issues

The pull requests are best to see what has been worked on and is waiting to be merged into the app. Anyone can participate.

You can search on the github page where you add requests.

You can see the list of bugs/feature request over on github: https://github.com/dessalines/jerboa/issues