When the ‘Lam of Ta’leel’ occurs in the Quran and it seems on the outside to ascribe motive to Allah, we say it is a Lam that shows consequence, not motive.
The link between a person and his adopted son (i.e. the perceived socio-genetic linkage) was fully broken both by the revelation and by the Prophet’s (ﷺ) marriage to Zaynab (RAA). Also note that when the Qur’an mentioned ‘fear’ in the context of the Prophet’s (ﷺ) marriage, it refers to shyness in front of people, not fear of doing what is right in Allah’s judgment.
The narration about the 7 Ahruf is in fact considered one of the Mutashaabihat that is one reason why there are 40 or more interpretations to it.
Adoption in the sense of taking care of orphaned children, etc., is very much allowed in Islam; yet depriving the child of his true lineage is forbidden.
One of the potential positive matters related to Husn ad-Dhann is that even if the person doing some outward good deed is doing it for ulteriorly bad motives, our good thoughts about him might transform his bad motives into good ones. Thus, we should avoid Suu’ adh-Dhann so as to not receive a bad verdict from Allah.
There is mention of the story of Sa’d ibn Abi Waqqas’ and Salman al-Farsi’s (RAA) armies during their campaign crossing the river with their horses (i.e. akin to walking on water) – this is one of the miracles (Karamaat) of the Companions.
At Badr, the Prophet (ﷺ) was already guaranteed victory, so why would he make such fervent Duas? Because the core of Dua’ is to show one’s servitude to Allah first and foremost, the blessings of Allah upon one are a secondary reality of Dua’ so as to say.