I challenge you!

So, will it be the same hero? In reserve? Won't they decrease in number for hiring if placed in reserve?I don't know yet if it's possible to summon a copy of the hero from reserve. And how many copies will need to be accumulated and placed in reserve. And having two identical heroes isn't good. I'll get to my home computer in the evening, and I'll probably check it, if someone doesn't get there before me :)
If this is possible, then it will be possible to calmly implement everything.

example: I add the hero Sarge (known as Axel) to the reserve, in the map settings, in the Heroes section, I put checkmarks on the heroes that will be available on the map, in the script I write:

player = {1, 2, 3, 4... etc.};
for i = 1, length(player) do
  AllowPlayerTavernHero(player[i], 'Sarge', nil);
end;

Yes, you can summon the same hero from reserve indefinitely. Regarding "I don't know yet if it's possible to summon a copy of the hero from reserve," I'm not sure, but it's easy to figure out logically for tactical scripts, i.e., using StartCombat... it's not summoned onto the map, which means that in fact, there will only be one hero on the global map. (as we know, there is DeployReserveHero for summoning from reserve to the global map, but it's not needed here)
80 heroes, this is if it's a standard set... I suggest making it simpler: take one hero for each faction, name them something like "Garrison Defender," and summon them :). Control their abilities and upgrades through scripts, depending on the difficulty or other factors, such as the day since the start of the game ;) (this option might even be more fun)