I would like to start building a Python app, not sure quite where to start.

There are probably resources out there that address this type of question, but I think the best answer is the quote from Arthur Ashe: "Start where you are. Use what you have. Do what you can." Don't wait to start writing code for fear that you'll have to rewrite it. Rewriting code is part of the process. Every time you go back to code you have written, you'll find areas where you could improve it based on new knowledge and experience you gained since the last time you worked on it. Sometimes you will learn something that makes you want to rewrite entire projects, and that's ok. Sometimes an update is made to the language that makes the way you wrote your code nearly obsolete, and that's also ok. The most important thing is to start creating your project and figure out what works and what doesn't. Figure out what you can do well, what you can do well enough to make it work, and what you still need to learn. You can always go back and make it better. If you're really worried about putting too much work into something and not wanting to re-write it, start with something small. As you add complexity, you'll find that there are different techniques and methods that are needed, and some of those will have nuanced ways of implementing them that make them better or worse for what you're trying to accomplish, but that's part of learning, part of coding, and part of life. Go make the world a better place by adding your code to it, and then in 10 or 20 years come back and complain that you wish you had known the stuff when you started. It may not be the best code, but if it solves a problem or makes life better, it's awesome, and it's an amazing feeling to know that you were the one that is responsible.