I've been able to fit three of those rooms into the primary hull roughly between where the phasers are on the dorsal and ventral of the saucer. The two giant vertical columns in the room could be the power feeds to the upper and lower phasers for each room. Alternatively, the forward room might be extra large because adjacent to it is the automated photon torpedo launchers in the ventral part of the ship... But yeah, they do take up a lot of space.
Which I guess is a good thing, as the sum total of the other sets doesn't necessarily add up to much. We would do well to speculate on extensive engineering and shuttle handling facilities beyond those established, to fill in the secondary hull - and mission-related facilities like these in the primary hull as well. Of course, ST:TMP shows and TOS already hints that recreation is another "mission" to which lots of space is devoted. But the three-deck recreation room indicated in both could be what takes up the aft sectors of the saucer (a bit off to one side, or perhaps both, if we take your neat idea for how Impulse Engineering is arranged) where these weapons-related facilities control the forward sectors. Crew cabins and the like would justly be squeezed in the cracks... Timo Saloniemi