You don’t need a formal business plan. But you do need a plan. So make two simultaneous plans.
Make one plan that depends on nobody else. No record deal. No investors. No lucky break. Your profits may be small but sustainable. Grow your audience. Develop your skills. Build your reputation. You can happily continue this way indefinitely.
Make another plan that uses the music industry. Build your team. Pursue a record deal. Find investors. Incease your odds of a lucky break.
Pursue these two plans simultaneously.
Then if a deal is offered to you, you can take it or leave it. It gives you great power in negotation. You become a better investment when you don’t need their money. It shows that you’ll be successful whether they’re involved or not.
If you’re prepared for either path, then your plan wins no matter what happens.