Re: The issue of Fadak
You have quoted a Sahih al-Bukhari tradition to prove a Shi'a belief?? That's a bit odd! Anyway, the Qur'an itself has confirmed that the relationship between Imam Ali (as) and Bibi al-Zahra (as) was PERFECT throughout. Thus, any narration anywhere that contradicts the Qur'an is false.
We read in the Holy Qur’an:
He has let free the two bodies of flowing water, meeting together:
Between them is a Barrier which they do not transgress:
Then which of the favours of your Lord will ye deny?
Out of them come Pearls and Coral:Al-Qur'an, Surah 55, Ayah 19 - 22, translated by Yusufali
Imam al-Suyuti in his Tafseer Durre Manthur, Volume 6 page 143, while commenting on the verse, states:
According to Ibn Abbas the two rivers mean 'Ali and Fatima. The barrier means the Holy Prophet and the pearl and coral mean Hasan and Husayn
As for the Sahih al-Bukhari tradition that you cited, it is weak on account of one of its narrators. Modern day Sunni scholar Shaykh Hassan Saqaf in his book Majm'o Rasael al-Saqqaf, Volume 2 page 738 stated on this alleged story:
وهو حديث شاذ تكلم عليه بعض الحفاظ !! لأنه من رواية المسور بن مخرمة وكان منحرفاً عن سيدنا علي.
"It is an odd tradition and some scholars reject it!! because it is narrated by Musawar bin Makhrama who was deviated from Sayedna Ali".
Another angle from which Sunni scholars rejected the cited story is:
ووقع في صحيح مسلم من حديثه في خطبة علي لابنه أبي جهل قال المسور سمعت النبي صلى الله عليه و سلم وأنا محتلم يخطب الناس فذكر الحديث وهو مشكل المأخذ لأن المؤرخين لم يختلفوا أن مولده كان بعد الهجرة وقصة خطبة علي كانت بعد مولد المسور بنحو من ست سنين أو سبع سنين فكيف يسمى محتلما
*In Sahih Muslim recorded his (Musawar's) tradition about Ali's proposal to Abu Jahl's daughter, he said: 'I heard the prophet (s) addressing to the people while I was adult'. There is a problem in accepting the hadith because the historians never disagreed about his (Musawar's) birth which was after the migration while the story of Ali's proposal is about six or seven years after Musawar's birth, thus how come he was an adult?'. *
That should be enough to keep your lips dry!