Is it permissible to follow the opinion of Sheikh al-Islam Ibn Taymiyyah regarding the omission of a condition for prayer due to ignorance, because of hardship or difficulty, and does this permission apply to multiple instances of ignorance concerning ablution (wudu') and ritual purity (tahara)?

The madhhab (definition) of Sheikh al-Islam Ibn Taymiyyah and those who agreed with him is that whoever omits a condition or a pillar out of ignorance of its obligation is not required to repeat [the act], whether the omitted part was in purification or otherwise. This is a strong madhhab, and there is no harm in acting upon it; it is not among the blameworthy concessions.