Yes, you can use personal money to pay for business expenses (just not the other way around.) In fact, most businesses start up this way with the owners putting their personal money into the business to get things started. In the end, the accounts track it all when they balance the books. If the money put into the business is more than the money you get out, it comes out as a loss for the year. But I do suggest you talk with an accountant.

keep personal accounting and business accounting seperate because there may betax benefits if you claim some expenses, you may claim some deductions based on your local tax law.

It would be best to get your own business account with your name as a DBA so you can deposit clients checks. That way your expenses are written out as a business expenses.

As for putting funds into your business you can do that. Most businesses owners fund their own business until they have cash from clients. I've done that before when I had to pay for a business expensive but didn't want to use my personal cards.

It is best to keep everything separate. Mixing business and personal assets can become a mess. If you ever got sued someone could pierce the corporate veil that way too.