Congrats on getting the model convertor guys! This will be a legendary mod when it gets finished. I was thinking about doing a similar mod but don't have the experience so I might as well throw some of my ideas out there for you.
So when I was brain storming on how to make it possible to have aircraft, I thought about how they would function since aircraft didn't do close air support during this time period. Instead they did recon, air superiority and some strategic bombing. So they need to be able to move around on the campaign map to scout, kill other aircraft, and perhaps damage structures.
We already have a unit that can do all that: The Rake. So my original idea was to change the Brothel into a military structure like an airfield or something, change the campaign map model, and then adjust Rake Spawn Rate and max Rakes. The player can then just build 'airfields' and get a complement of 'airplanes'. You can even have famous pilots since all Rakes are named and have varying levels of skill.
While there are some problems, I think this would work pretty well. Just don't forget to change all gentlemen to imams so they can't duel airplanes.
Go Go Red Baron!