Try to make something challenging, but try to be reasonable to keep yourself from feeling overwhelmed.
If you feel a lot of resistance towards working on a game or jam then you should just start small, anything is a win and you can build on it in the future.
Planning things out properly helps a lot to get a better mental image for your game and scope, it helps you to see the steps and process more clearly.
Working with others is always an option and might allow you to focus more on a particular skill.
If it doesn't work out it's ok.
But you sound motivated to me, at the end of the day if you don't try, you won't know.