Visual Guessing
Logistically, I believe the shuttle bay could effectively hold four spirit dropships and eighteen banshees without excessive clutter. Two drop ships at mid-level combat ready and two at the top ready to load. Nine banshees on the floor per bay. Alternatively, two seraphs may replace any dropship or nine banshees. I estimate that battlecruisers have four hangars with a total of eight seraphs, sixteen dropships, and thirty six banshees. If I recall correctly, these numbers would roughly match the complements on UNSC cruisers. Also, such numbers seem to fit the craft density in Halo: CE's campaign. Based on the landing pads of Phantoms in High Charity it could be assumed Phantom physiology would not conform well to the current structure of hangar bays seen so far in Halo.