1. I have a criminal record on minor drinking. (I was 19 yrs old.) I
pled guilty and paid $150. It was in 2002 while I was a sophomore in
college.

2. I'm applying for lawschool. How much does this will affect my
prospect of getting admission successfully? Any friend of yours who
had this level of record and got into law school with no problem?

3. What about its impact on my passing the bar, given their fitness test?

4. Is expunging this record necessary? Or is it common that most
Americans carry this sort of criminal record with them? (I am a
foreigner.)

19 is not a minor.  It was underage drinking.  You were an adult at
the time.  Sucks, I know.