Is it obligatory to perform ablution immediately upon passing wind during ghusl, or can it be delayed, and does minor ritual impurity invalidate ghusl?

Ablution (Ghusl) is not invalidated by minor ritual impurity (hadath asghar) during its performance, and there is no need to repeat it. If wind is expelled, the ghusl is not to be repeated. However, if ablution (wudu') is broken after washing the parts of the body required for wudu' during ghusl, then wudu' is obligatory for prayer after the ghusl. The fundamental principle is that ritual purity remains when in doubt, so fleeting doubts should not be entertained.