Have you made any progress with your 0concepts? They sound very interesting. I particularly approve of the idea that offered contracts should be driven by the service you offer. But that in itself should be reflective of the region where you operate: ie what is the local market?
A decision to make it off-line as well is a good one too. I use OnAir which is online and where you nominally compete or collaborate with other businesses. But the reality is that despite some real effort by the Devs to make this aspect work, there really is very little interaction to make the drawbacks that come with an online MMO worth it. Part of the problem is, I suspect, that the flight sim is too niche and the lack of direct communication in-game/flight with other players. But offline shouldn’t mean isolated - a competitive element is always good.
The keys to any successful game is that fine balance between risk and reward. The snakes and the ladders. This is where the economic model used needs very careful design and balance.
Conceptually though I suspect what most flightsimmers want isn’t a business simulator it’s a mission generator. I may be projecting my own views here, but what I’m looking for is something that gives me credible missions/tasks that I then have to undertake realistic flight planning and management of operational assets to complete, with benefits and rewards for doing so. In short, something that gives real purpose to flying.