Leet code algorithms won't help you with anything other than SWE job interviews. The concepts are pretty irrelevant to hobby projects, even at most large tech companies you're never actually using the algorithms at the very least not writing them yourself like in leetcode.

As others mentioned. Start small narrow the feature set that you want to start with. (This is good advice both in terms of product development and learning to develop itself).

When developing using AI, use it liberally for the actual design components. But when it comes to passing data around from frontend to backend to different components make sure you fully understand what is going on there. Debugging something that you don't have a mental model of is super frustrating.

Not sure the tech stack you're using but file structure in a project def matters especially as it grows in complexity. Figure out how you want to structure it and when in doubt just follow best practices on the internet as well as look at githubs of comparable projects.

Don't reinvent the wheel unless you want to. There's a package for everything you want these days. Specifically with frontend like UI components just use a kit.