Many organizations that distribute Matanot L’Evyonim solicit donations from people before purim, but distribute the money collected on Purim.
Is it acceptable to donate to one of these organizations, or is it required to actually give the money to the organization on Purim day itself?
Giving before Purim to be distributed on Purim is fine too.
What’s the minimum amount to give to fulfill the mitzvah?
There’s no specific dollar amount. Whatever you are comfortable giving
any difference if the evyon is goy or yid in order to fulfill the mitzvah on purim?
The poor person should be a Jew
Where is the source for it being a Jew?
Megilath Esther.
Chapter 9, verse 22