1. Jupiter Notebooks are kind of more for interactive use, as basically they're an enhanced version of the Python shell. Use a regular text editor for real programs like this. I'd do Git too actually. At the very least, if you have a repository on a place like GitHub, you have a backup for free. Version control is undoubtedly a useful skill in any case.
2. The Python standard library includes a module for reading and writing CSV files, so you could use that. You might also consider using a database, though that requires more learning on your part. Python comes with support for the database SQLite, which is a small, file-based relational database.
3. If you're just a beginner, I'd stick to thinking about the terminal for now. GUIs and phone apps are going to be more complicated and I'd think that's too much in one go.
2. The Python standard library includes a module for reading and writing CSV files, so you could use that. You might also consider using a database, though that requires more learning on your part. Python comes with support for the database SQLite, which is a small, file-based relational database.
3. If you're just a beginner, I'd stick to thinking about the terminal for now. GUIs and phone apps are going to be more complicated and I'd think that's too much in one go.