Interesting. It'd be tough to forgo a "Big Week" type scenario Feb '44, though. Starting in Sep '44, almost excludes the P-47D-11.
Not sure what the time frame will be, but to maximize the idea of aircraft model upgrades, at least for the US FGs, I'd recommend a Big Week frame (Feb '44), a D-Day frame (June '44), an Oct '44 frame, and then a post Jan '45 frame to include the P-47M for the 56th FG.
Not sure how those dates would affect the Luftwaffe Order of Battle though. And it depends on which US FGs they decide to include. With the 56th, you get the best range of P-47 models, there are many skins for the 20th FG P-38Js and you get some nice P-51D skins too. It'd be tough to exclude the 4th, 352nd and the 357th FGs also. Such great skins available for those groups.
I'm working on another spreadsheet that shows which skins we have available within this framework too - that may help the decision of which FGs to include.