What is the difference between Ahl as-Sunnah wa al-Jama'ah and other legal schools of thought, and is it permissible for a Sunni girl to marry a man who does not belong to a (Sunni) legal school of thought?

Ahl al-Sunnah wa al-Jama'ah are contrasted with Ahl al-Bid'ah wa al-Dalal (people of innovation and misguidance) in creed and methodology, such as the Ash'aris, Mu'tazilis, Murji'ah, and Sufis, not the jurisprudential schools like the Hanafis, Malikis, Shafi'is, and Hanbalis, whose imams are from Ahl al-Sunnah. The fundamental principle is that a Muslim should adhere to the Qur'an and Sunnah according to the understanding of the righteous predecessors (Salaf as-Salih). It is neither obligatory nor recommended to adhere to a specific madhhab (school of thought). Whoever adheres to one particular madhhab exclusively is a mistaken bigot. It is permissible to follow the four madhahib for those who cannot deduce rulings themselves, but it is obligatory to follow what is correct once it becomes apparent. The Qur'an condemned those who turned away from following the messengers to what they inherited from their fathers' religion, and this is the forbidden taqlid (blind following). However, it is permissible for someone incapable of independent reasoning to imitate (follow) a scholar. The taqlid forbidden by text and consensus is opposing the word of Allah and His Messenger with something contrary to it. The followers of the Salaf are those who remained steadfast upon the Qur'an and Sunnah in creed, jurisprudence, and conduct. If a Muslim woman is proposed to by someone whose religion and character are pleasing, she should accept him, even if he does not ascribe to a specific madhhab. However, if he belongs to one of the misguided sects, she should not accept him.