Before you write a line of code, make a clear decision as to whether it's a learning experience or a business venture. Plan your project based on the goal you've chosen. If it's a learning experience, consciously avoid doing anything that doesn't push you to learn something new. If it's a business venture, consciously avoid doing anything unless you believe it has the highest RoI.
Some purely recreational projects do turn into viable businesses, but far more projects have failed due to indecision and yak shaving. If you're building a business, you don't gain anything by experimenting with a new stack. If you're learning React, you don't gain anything by writing a bunch of CSS and marketing copy. Don't be afraid to step away from the keyboard and ask yourself "Is this a good use of my time?".