Pre-Approval

Hello, I am a first time home buyer looking at buying a condo in Manhattan. I have a few questions - How many banks should I approach for pre-approval? Any recommendations on the best banks to work with? Should I also look at Credit Unions? If so, does any of you have any recommendations? Does applying at multiple banks impact my credit score? I read somewhere that it will be counted as one hard inquiry if I apply within 2 weeks but wasn't sure if there is a limit. Any advice will be appreciated. Thanks!