Yes, someone who is legally responsible to pay Zakat can pay through monthly instalments throughout the year, with the intention of paying Zakat. When lunar year comes to an end, Zakat should be calculated, and whatever remains outstanding should be paid off. In similar fashion, outstanding amount can also be paid through instalment.

Yes, in order to fulfil one’s obligation, one must intend (i.e., specify) that they are paying Zakat. As an act of worship pertaining to financial dealings, an intention is required in order for it to be performed correctly. The intention (niyya) for fulfilling one’s obligation is to intend that one is paying Zakat, whether that be at time of distributing one’s wealth to those who are eligible (i.e., at the time of payment), or when setting Zakat money aside.

If these valuable stones and jewels [i.e., other than gold and silver] are for the purpose of trading, then they are liable for Zakat. If however, they are used for one’s personal use, Zakat does not need to be paid on it, irrespective of its value.

Zakat becomes obligatory if someone is minimally in possession of 612.36 grams of silver. One-fortieth (1/40) of the total amount should be paid as Zakat. Abu Sa`id al-Khudri states that Holy Prophet [SAW] said,

There is no Zakat upon any silver that is less than five awqiya (612.36 grams) [Bukhari, #1390].

It must be noted that the Zakat due is equivalent to 2.5% either by weight or value.