(2) Is it mandatory to use soap/body wash for washing body in fardh ghusl?
(3) Is it mandatory to pour water 3 times over the whole body during fardh ghusl?
(4) In fardh ghusl when I pour water over my body if some drop of water or soap foam falls into the bucket from my body then water of the bucket remains pure for ghusl or not?
بسم الله الرحمن الرحيم
(1) The said method of ghusl is correct.
(2) The use of soap is not necessary, you may also have ghusl without soap.
(3) It is not necessary three times, if water reaches over the whole body once then it is enough but it is mandatory that no part of the body is left dry; hence it is sunnah and mustahab to pour water thrice.
(4) According to preferable saying the used water is pure hence if used water of body or the foam of soap falls in the bucket then the water of the bucket shall not become impure provided no impurity is mixed with the used water.
Allah knows Best!
Darul Uloom Deoband