If you quit you employment, the loan must be repaid immediately. If you don't the amount borrowed is treated as an early distribution and is taxable. Many foundations provide funding in the form of grants. These should be used with care because of the excessively high rates of interest usually charged. Best way to determine what kind of business to start is to look to your own interests and abilities.
Interest is paramount and the expertise can be learned.
Research your interest or consider a trade school or community college. Use the Internet to search for web-based training on a variety of subjects. Keep your eyes and ears open - there are opportunities everywhere. Talk with friends and associates about starting a business. Review the many magazines devoted to small business and entrepreneurs.