That is a major life-change and should not be done on a whim. First study Judaism in depth and make an informed decision. Conversion according to Torah-procedure requires the intention to observe the Jewish laws. In addition, female converts undergo ritual immersion, and male converts are also circumcised.
According to Jewish law, a Kohen can't marry a convert to Judaism.
He didn't.
Nothing. Jews do not seek converts. If a person wishes to convert to Judaism, they are permitted to do so, but Judaism teaches that Judaism should not be proselytized.
No, Obama is a Christian.
yes
Yes, according to tradition.
Only Judaism
His father is a convert to Judaism and his mother is Jewish.
A new Jew.
Lots of reasons. One is that Judaism doesn't believe in encouraging people to convert. If someone wants to convert to Judaism, they're welcome to (although discouraged at first), but Judaism has no mass programs to get people to convert. Nor did it usually have forced conversions like the other religions did. Another reason is that Jews have been heavily persecuted over the years and many were killed.
His father is Jewish and his mother is a convert to Reform Judaism.
Jewish people would call it apostasy.