Firstly, thank you for responding.
Having players identical would even the playing field and reduce problems with people wanting to be specific players. I support that idea.
Controlling/using players should be similar, but should the player's identities be similar? Or should players be able to customize them?
Minidungeon at start, however, sounds totally unbalanced. If you don't expect them to survive, what is the point of the overlord? What you should do is a simple setup timer gate instead, even though it's already been done in other games. Just because it's already used in other games doesn't mean it's not a candidate.
Not sure if I made this clear enough, but the mini-dungeon doesn't count towards the actual game. To re-explain it, at the start of the game, players spawn in the mini-dungeon and rush to complete it. If they die, it doesn't count against them and they simply respawn. If the players reach the end before the time runs out, they are rewarded with some sort of perk or something. If not, they don't get anything. Once the time has run out, all the players respawn at the start of the actual map and from there on, actually play the game. The point of the mini-dungeon is so that the Overlord has time to set up in the beginning of the game.
Variable minion strength sounds bad as players won't find difficulty consistent with looks. What you should do instead is have zones of circles with the overlord at the center, and assign a specific set of units to each zone. They can b of the same types but should have at least one major visible difference between them, such as color.
Instead of the minions changing looks, the scenery will. For example, minions will be weakest towards the starting area of the game. This area will generally use light colors. Medium strength minions will be found in the dark color areas. Strong minions will be found in the gray, death-filled final areas of the game.