Some questions about names...

I am planning to study in an American University when I get old enough. I have been trying to come up with some good English name that could be used. My Last name(which I heard, is unchangeable) is Im, rhymes with brim. I have several questions to ask of you smart people :)
1. My current idea for my name is Martinez. Does this sound good?
2. Can you guys suggest any names that suggests friendliness and easy-going nature? I hope its longer than 5 letters because my last name’s kind of short and I want to compensate for it…
3. Does having different names affect one’s interview by even the tiniest bit? I heard that some names invoke certain ideas or feelings in people… dunno why…