Should I start my business plan so I can get a loan from banks and etc.

I have a phone repairing company that may extend to do more things that requires me to have cell phones on hand should I write a Business Plan and send it to banks so I can get a loan or should I use my own money to build up from it. I am currently $250 dollars away from having my business be an official LLC of New York and business is getting hot so far. I don't have a business credit card or checking account also.