Regarding the corridors leading to the hangar deck I'm under the impression you had rationalized this by having several different decks leading to the different levels of the hangar deck. Wouldn't just one be sufficient?
The (tighter) circular corridor arround the "yellow circle" at the bottom of the engineering hull could have been the one Matt Decker arrived on in "Doomsday Machine". There he took a corridor leading to the port side of the ship and made his way to the shuttle repair shops using a corridor close to the outside of the ship.
The circular corridor segment (curvature of actual studio set) with a turbolift on the port side McCoy and Spock arrived in "Immunity Syndrome" is further back to the stern of the ship (it's probably the same corridor segment Kirk, Spock and McCoy used in "Journey to Babel").
While it is odd that Kirk and Spock used a different route in "Let That Be Your Last Battlefield", that corridor piece suggests another doorframe (starboard right next to the one from IS and JB), but it also leads to the same hangar deck main door.