Should a preacher not call for something until he considers its outcome, and how sound is the jurisprudential maxim that states: "Establishing a ruling is different from applying a ruling"?

It is commendable that you are concerned with da'wah (calling to Islam) according to the methodology of the Salaf (pious predecessors). However, it is imperative that the da'i (caller) acts upon what he preaches. Nevertheless, an imperfect commitment does not negate the obligation of da'wah. The caller should mix with people, not isolate himself from them, as this was the guidance of the Prophets and the Companions. Al-Wala' wal-Bara' (loyalty and disavowal for the sake of Allah) do not necessitate abandoning social interaction. Adherence to acts of obedience is the key to sustenance and blessing in this world and the hereafter, and it is not permissible for the caller to be negligent in acts of obedience due to his busy schedule.