Scope of work would benefit from consulting an architect.

There is no problem in doing this, as long as there are egress windows where needed. The definition of "mezzanine/ loft" doesn't really have any practical applications here. It is simply a habitable space.
HABITABLE SPACE. A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable spaces.


http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_2_sec002.htm

There is no "official definition" of "bedroom".
A sleeping area has to meet additional requirements to that of a habitable area such as smoke detectors, minimum square footage, ceiling height, ventilation, and an emergency escape and rescue opening, etc.


http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_sec010.htm