You have mistaken Khums with Zakat.
Khums is obligatory on the following seven things:
1)Profit or gain from earning.
4)Amalgamation of Halal wealth with Haraam.
5)Gems obtained from the sea diving.
6)Spoils of war.
7)As commonly held, a land which a zimmi (a non-Muslim living under
the protection of Islamic Government) purchases from a Muslim.
As you can see just we are commonly obligated to take care of the first one (Profit or gain from earning.)
3.There are many rules regarding how and when one has to pay khums on Profit or gain from earning but the first and most general rule is that
if a person earns by means of trade, industry or any other ways
of earning, like, if he earns some money by offering prayers and
fasting on behalf of a dead person, and if it exceeds the annual
expenses for maintaining himself and his family, he should pay Khums
(i.e. 1/5) from the surplus.
For the detailed rules please visit: http://www.sistani.org/english/book/48/2286/
4.Khums should be divided into two parts. One part is Sehme Sadaat, it
should be given to a Sayyid who is poor, or orphan, or who has become
stranded without money during his journey. The second part is Sehme
Imam (A.S.), and during the present time it should be given to a
Mujtahid, who fulfils all conditions or be spend in the ways allowed
by that Mojtahid. Regarding the first part khums can be spent, for
such purposes by the permission of that Mujtahid. As an obligatory
precaution, that Mujtahid must be Aalam, and well versed in public
5.If the wife of a person is a Sayyidah, he should not, as an obligatory precaution, give Khums to her for meeting her own expenses.
For more detailed rules please visit: http://www.sistani.org/english/book/48/2293/