What programming language should I choose for my app development goals?

Python might be a solid choice for what you're trying to achieve. If you're exploring mobile app development, Flutter with Dart could also work well for creating cross-platform apps, but since you have some experience in Python, it might be best to stick with that unless you have specific requirements to change.

Why not try existing solutions? If your main goal is to enhance your programming skills while creating useful tools, then dive into this project! But if you're only after functionality, check out established apps like Notion or use tools like Obsidian with plugins to keep your projects organized.

Consider FastAPI if you're leaning towards Python; it's great for building APIs. However, if you just want something to manage budgets or household items, there are existing apps that might fit your needs better.

If you're looking for something that's easy to manage locally, Java could be a great fit. It's really portable due to the JVM, and building an Android app with Java is fairly straightforward for someone who's creating a local solution.

You could go with Python or even combine Node.js with React for the front-end. It all depends on whether you want a locally hosted solution or something browser-based!