To get a mortgage from a traditional lender...yes. Your mortgage must meet guidelines so they can resale your mortgage later. It is part of their business.
What is a "good" credit score? That will very depending on whom you speak with. Conventional mortgages require higher scores, FHA can be obtained with lower scores...but have higher cost. Some lenders have options for non-conventional loans that would allow lower credit scores, but likely will require larger down payments and would carry a higher interest rate.
Best advise, speak to a mortgage officer that can discuss your situation and explain the process. If your scores are low, make a plan to get them up so you can obtain a great mortgage. Save your money and be patient. I have a few great lenders on my web site if you need to speak to someone.
Bernstein Realty, Inc.