A centrally located facility would probably make the most sense, as the ship does supposedly have phasers all over, despite only a few under-saucer firing locations actually being seen.
The problem with this is that a facility equidistant from all phasers is just another remote console. Why is this remote console necessary for firing at the Romulans - why not a console on the bridge? It would make technological sense if Spock had to hurry down to physically pull some key lever that moves some heavy mechanical component or something, but Spock merely pushes buttons; by all rights, he should have been able to push such buttons on the bridge, too.
As for the walkarounds, it would certainly make good sense to have a ladder shaft that connects the decks and
is isolated from each deck by an A-frame pressure door. Making this a simple vertical feature and still remaining true to the sets may be impossible - but a zigzagging staircase also makes great sense.