Perhaps some inspiration is to be found in the way Civ V handled international projects? A much longer-burning version of that, with mini-project milestones that trigger the creation of each hero, granting benefits to the civ that 'wins' each milestone (thereby 'training' each hero) as well as contributing to the larger-scale goal of Assembling the heroes? ...I'm just spitballing, probably absurdly; I have zero programming knowledge and know nothing at all of what I speak.
The idea also reminds me of Mass Effect 3's interspecies galactic cooperation effort against the Reapers, though that's far afield of the programming mechanics here.
The idea also reminds me of Mass Effect 3's interspecies galactic cooperation effort against the Reapers, though that's far afield of the programming mechanics here.