Do we know when Birkat haTorah was composed and added as an obligatory blessing to be said before learning Torah? Is it just something done by Anshei Knesset haGedolah or do we have any other information relating to its authorship, the period in time when it was adopted, etc?
The Ramban holds that Birchas Hatorah is biblically mandated. Accordingly, some form of Birchas HaTorah would have existed from Matan Torah. (However, this doesn't necessarily mean that the Nussach is d'Oiraysa.)
The exact classification of the three Berachos of Birchas HaTorah are subject to much debate among the achronim. If any of them are Birchas HaMitzvos or Birchas HaNehenin, they would not have been around until the Anshei Kneses Hagedola instituted them. [The Ramban is referring only to whichever part of Birchas Hatorah is derived from the verse כי שם ה׳ אקרא הבו גודל לאלקינו.]