You might wish to look at a tafseer of Ayat 89 of Surah Maidah for your answer as it deals with the topic.
To the best of my (admittedly incomplete and possibly inaccurate) knowledge, feeding means feeding each one of the ten poor people two full meals (breakfast and supper); or one of them twenty full meals. There are also fixed amounts that can be given in various foods ie. dates, wheat, etc or the equivalent price of any one of them. (I am unsure of the amounts as they are in sa'e)
You can also clothe ten poor people.
I am not sure if the poor people have to be Muslims.
Fasting three days is only allowed for those who cannot afford the other two choices. And the three days have to be back to back.
FYI Kaffarah/repentance can only be given after breaking the swear. You can't give the Kaffarah and then break your swear.
This information is taken from the Hanafi book of Fiqh 'Qudoori' and its commentary 'alLubaab'