ORIGINAL: Don Bowen
Doesn't directly answer any of the questions, but very interesting - thanks.
It does mention one factor that's going to be the salient factor in the rework - the hangar deck was the strength deck on the Essex, everything above that is superstructure, whereas on the UK CVs the strength deck is the flight deck. Trying to replicate that would mean a fundamental change in the Essex design and all of the stress and strength calculations would need redoing from the bottom up - effectively you're designing a new ship. So presumably what we're looking at is instead a reworking in which the strength deck remains the hangar deck, but plating is simply laid on at flight-deck level. That would likely also mean that the supporting structure for the flightdeck would need reinforcing, so it isn't simply a one-for-one swap of wood-decking for STS, but it's close. Equally the hangar sides would need to change, the USN used an open box hangar to allow aircraft to warm up before they were brought to the flightdeck, the RN relied on a sealed armoured box hangar and the Iwo Jima would need armoured sides to get the full benefit of the armoured deck, which is rendered pretty pointless if the kamikaze flies into the hangar from the side... Enclosing the hangar would mean slower flight ops and force the Iwo Jima to operate more in the RN fashion. Other changes are pretty much incidental.
The only parts of this that WITP AE simulates are deck and belt armour thicknesses, it doesn't simulate having two deck levels and different levels of protection for each, it doesn't simulate different armour levels between belt proper and hangar side, all we can do is boost the deck armour level by 38mm (1.5in) and maybe the belt armour as well.
(And of course the irony is that just as the USN looked at British style armoured hangars the RN was seriously looking at moving to US open hangars with the Maltas)