1) One for it is Sunnat-e-Muakhidah Ala Kifayah
2) Not advisable.
3) Some permissible, others not proven. When one studies the Itikhaaf of Nabi (S.A.W) then none of what has been stated can be authentically and reliably proven. It has been introduced these days to keep those performing Itikhaaf engaged in some Deeni activity whereas is subsequently defeating the very purpose of Itikhaaf, which is seclusion and seeking for the night of Qadr.
These days it has become a gathering of merry making, eating, wasting time, money and energy.
The whole matter needs reviewing carefully. Huge numbers sit, all sorts of activities are done, the effects are temoprary on that which is not proven in Shariat.