From: Hessen, Germany - now living in France
VP-21 should be there from the start because that's where it was historically.
And there should be the ability to stage in aircraft, because historically B-17s had been ferried before the war from CONUS via PH, Midway, Wake, Port Moresby, Darwin to the Philippines.
However, those planes were just staging through Midway on a ferry flight, their servicing was limited to refueling by the Marines present at Midway and none of the staging bases had the infrastructure nor the avgas / bombs nor the ground crews needed for a combat deployment.
Therefore, Midway should not have an USAAF base force but a Marine Corps or Navy base force with some limited AV support.
In the game, Wake has a CPNAB base force with 12 AV support, representing the civilian contractors building the base facilities and probably the PanAm Clipper base. Something similar could have been done for Midway, since it also had CPNAB and PanAm present.
But the presence of the USAAF base force at Midway is propably a concession to the AI in Japan vs. AI setups.