Is it permissible for an educated person who is not specialized in Fiqh, and who has not studied according to one of the four schools of thought, to choose from the Fiqh of the Sunnah what suits him from different opinions on a jurisprudential issue to act upon?

A student of knowledge acquires knowledge from its people, not from books. This is because deriving rulings from books without a shaykh requires knowledge of the language, the terminology of the jurists, and familiarity with some rulings. Furthermore, examining disputed matters is not the task of beginners.