If you don’t have an LLC, you can use your personal credit cards, but the onus will be on you to separate the charges.
Quarterly taxes are due 4 times a year. They don’t follow the standard calendar quarter schedule though.
A corporate structure’s job is to shield you from the liability of the business.
It basically allows you to become a regular employee of your company with a periodic paycheck and W2 at the end of the year at a salary that you determine.